Tutorials/Drowned farming

Drowned farming is a way to harvest experience orbs and loot dropped by both zombie and drowned mobs. In addition to explaining general mechanics of drowned farming, this tutorial describes two basic drowned farms that are easy to construct in survival mode, without needing a villager as bait.

In all editions, the simple flooded-dungeon farm described first produces the usual rotten flesh, gold, armor, and weapons dropped by zombies, as well as experience orbs and copper ingots dropped by drowned, but not nautilus shells or tridents. $$ this farm also produces nautilus shells, but not tridents.

The aerial farm (described second) produces only drowned drops including tridents, but not zombie drops. While the aerial farm doesn't require exotic materials, it does require large amounts of materials and is more time-consuming to build.

More complex farms are possible, particularly underwater farms for naturally-spawned drowned, which also yield tridents and nautilus shells. The simple survival-mode flooded-dungeon farm described here is still useful for gaining a quick and easy way to harvest experience and zombie drops without requiring significant construction or materials.

Mechanics
There are three main ways to farm drowned, depending on the Edition and which drops you desire most. In most cases, it's a good idea to kill the drowned manually to obtain the more valuable loot.

Flooded dungeon
The detailed instructions in this tutorial explain how to use a flooded dungeon that converts zombies to drowned. This is the easiest method to implement in survival mode.

$$, this farm produces the usual zombie drops as well as experience (XP), but it doesn't produce the tridents and nautilus shells specific to drowned. In Bedrock Edition, this farm does produce nautilus shells but not tridents (zombies converted to drowned no longer drop tridents as of Bedrock Edition 1.16.0).

A flooded dungeon works by spawning zombies from the monster spawner in the dungeon. The zombies are funneled into an underwater chamber where they drown. Once converted to drowned, the player can manually kill them for their loot and experience.

The advantage to the flooded dungeon farm is that it produces potentially valuable zombie drops, such as iron swords and shovels, chainmail armor, and gold armor &mdash; any of which may have valuable enchantments. The disadvantage is that it does not produce tridents in any edition, and does not produce nautilus shells in Java Edition. However, it does produce copper ingots in both editions, as well as nautilus shells in Bedrock Edition.

Aerial
An aerial farm is probably the most practical way to farm tridents. It works by spawning drowned naturally on an aerial platform at least 24 blocks above the player, with the player being beyond the maximum spawning range of any other spawnable surface in the world. The drowned spawn naturally under the correct conditions of being underwater at light level zero, and they are funneled first into an intermediate area to prevent lethal fall damage, before dropping into the killing chamber where the player waits. The farm described here takes advantage of a mechanic $$ whereby a single layer of water causes an increasing reduction of light level with depth below that layer; the drowned spawn on a wet platform some distance under a glass-bottomed pool of water. $$, two layers of water may be needed for the platform to spawn drowned.

The disadvantage to the aerial farm is that it produces only drowned drops, but not zombie drops. As such, it is a good source of nautilus shells, tridents, and copper ingots, but not the valuable zombie drops such as enchanted items and armor made from iron or gold.

Underwater
An underwater farm is another way to farm tridents. Drowned farms in a body of water are more complicated because they function similar to a dry-land mob farm.

In an underwater farm, naturally-spawned drowned are attracted to a location and funneled into one area where the player can kill them. A villager is typically used as bait to attract drowned, and the funneling can be accomplished with bubble columns. Transporting a villager to an undersea room in survival mode is a complex undertaking that requires much forethought, preparation, implementation time, and risk.

Instead of a villager, a turtle egg might also work as bait, although this is less reliable because drowned don't detect eggs as they do villagers; they must first happen to look in the egg's direction, then have a clear path to the egg, and the egg must have sufficient space above to allow trampling on it.

Like an aerial farm, an underwater farm does not produce zombie drops, only drowned drops.

Location
The simplest way to start a survival-mode drowned and zombie farm is to locate a dungeon room that contains a zombie mob spawner. Ideally the room should be reasonably close to the overworld surface, but can be any depth that allows for digging 5 blocks or so underneath the floor. Sometimes a dungeon is found a short distance inside a cave entrance. Unlike an XP farm that generally requires a long falling distance from the dungeon to bring the mobs to near death, no deep excavation is required for a drowned farm.

Preparation
To construct a survival-mode drowned farm, you need a conveniently located dungeon with a zombie monster spawner, as well as a good weapon to clear out the dungeon, a cheap weapon to harvest drowned, torches, pickaxes, a water bucket, and a few signs. Optionally, glass blocks are helpful for viewing when a zombie becomes drowned. Hoppers and a couple of chests also aid collection but are not necessary.

For convenience, it is nice to have nearby (outside the dungeon room), a source of water to scoop with the bucket, gates or doors to keep mobs from wandering into your cave while you work, and a home base or temporary base with your bed, crafting table, and other helpful items a short walk away.

Construction
The illustration on the right shows a side view of a basic survival-mode drowned farm, showing the dungeon above and the trap / collection room below.

Prepare the dungeon
Upon locating a dungeon and breaking into it:
 * 1) Quickly place a torch on the mob spawner block to prevent it from spawning further zombies.
 * 2) Use your good weapon to kill any remaining zombies in the room.
 * 3) Close off any holes in the walls other than the entrance way you intend to use to get in and out of the room.
 * 4) Ransack and collect the chests for later use.
 * 5) It is not necessary to dig out the floor around the mob spawner, but doing so lets the spawner use its full vertical spawning volume. Digging out two layers allows mobs that spawn upstream of the spawner to be be swept underneath without getting stuck. You may also optionally expand the room to 4 blocks horizontally from the monster spawner block (a 9×9 room). The room still produces more than enough zombies without these expansions, however.

Take note of the coordinate location of the center block along the wall with your opening. This floor block is in line with the mob spawner. In the last step, you flood the dungeon with water and dig a hole in this location for the mobs to fall through.

After preparation, exit through your opening. Don't close it off yet.

Prepare the trap
Next, underneath the dungeon, excavate the trap room. The room should be large enough to move around in, and contain the trap described below.

At the most basic level, the trap consists of a single water block that the zombie falls through from above, landing on a block (or a hopper) so the zombie's head remains in the water and drowns it. A sign on the wall holds up the bottom of the water block, and solid blocks enclose the water on all sides. The enclosing blocks may be glass to aid your identification of drowned zombies versus non-drowned zombies.

With a one-water-block trap, zombies just crowd into that one-block space, making it difficult to target the drowned zombies with your weapon. Allow the zombies to spread out as they drown by extending the trap to multiple blocks. In practice, a trap using a two-block water channel held up with two signs, with two landing blocks (or hoppers) below the channel, works sufficiently well. The illustration shows a design using a three-block water channel, three signs, and three hoppers.


 * 1) Place blocks (preferably glass) on the ceiling to contain the water channel. One long side of the channel can be bounded by the wall of your room. The channel should be directly below the floor block previously measured in the dungeon above. This is where the water falls through into the channel.
 * 2) Place signs along the wall. The signs hold up the bottom of the water blocks while providing air space for you and mobs to pass by the signs.
 * 3) Using a water bucket, place a block of water on each end of the channel. If your channel is 3 blocks long, you need only two water blocks; the center block fills itself in. The channel must be completely full of still water. Running water allows for some breathing space; you want to avoid that.
 * 4) Only after filling the channel with water, place the hoppers under each sign, pointing toward the chest at the end of the line. Be outside the channel before you install the hoppers, lest you end up drowning yourself.
 * 5) * Hoppers are needed only to collect drops and move them into the chest.
 * 6) * If you can't afford hoppers (due to the amount of iron required), you can use stone blocks. In this case, just dig a 1-block trench next to these stone blocks so that you can fit underneath the overhead slabs, to get close enough to the dropped items to collect them yourself.
 * 7) Place slabs underneath the glass to create a half-block high space, enough for you to swing a sword at the drowned's legs, but not enough for baby zombies to slip through.

Start the farm
Finally, go back into the dungeon above.
 * 1) Place two water blocks, one at each corner opposite your entrance opening. The water should completely fill the room, sweeping you toward the entrance. If you have expanded the room and the water doesn't cover the whole floor, you may need an additional water block on each side wall, or build a stone structure in the far corners for the water to cascade down and spread more. If you stand anywhere in the room, the water should push you toward the center of the wall at your entrance hole.
 * 2) Stand on the threshold of your entrance, out of the water, to avoid drowning yourself in this step. Dig out the floor block at the center of the wall, causing the water to spill down into the channel in the collection room below. The reason to dig this hole after flooding the dungeon is because placing a water block near a hole causes the flow direction rules to prevent the water from covering the entire room.
 * 3) Break the torch on the mob spawner. A zombie spawns the instant the torch breaks. Quickly seal the opening of the dungeon. You can seal it with glass blocks as shown in the illustration, to let you see into the dungeon. You can recover the torch from the chest below.
 * 4) If no zombies spawn, the light level in the spawning room may be too bright. Adjust your arrangement of torches outside the room accordingly.

Operation
Go down into your collection room. As zombies fall into the water-trap channel, they wander back and forth across the tops of the hoppers with their heads in the water channel. After 30 seconds of having its head submerged, a zombie starts to drown, quivering visibly for 15 seconds, and then changes color. Its pants turn from blue to greenish. Its eyes, visible through the glass blocks, also change to a blue glow.

The legs of the mobs are exposed to you. With your cheap weapon, or even bare hands, whack at the legs of a drowned. Four hits with a stone sword can kill it. Experience orbs float toward you, and the drowned's possessions drop into the hoppers and end up in the chest (or if you didn't use hoppers, the drops come to you if you get close enough). Eventually nautilus shells, as well as copper ingots, armor (leather, gold, and chainmail, often enchanted) appear in the collection chest along with rotten flesh and miscellaneous other items.

The chest fills quickly because weapons and armor each occupy their own inventory slots. You may find it useful to have a garbage disposal hole in the ground somewhere in the room in which to throw unwanted items, which despawn after a few minutes in the hole. You can combine unenchanted armor and weapons in a grindstone to repair them, thereby saving space in your chest.

Baby zombies occasionally spawn, but they don't drown because they're too short. Simply kill these when they appear. The slabs under the glass blocks prevent them from escaping, and also prevent them from attacking you (although they can still hit downward if you get too close). Zombie villagers also spawn occasionally, and can be killed immediately because they don't drown.

To bypass the mob cap, make sure that part of the drowning platform is outside the 9×9×9 volume (in Java Edition) or the 16×10×16 volume (in Bedrock Edition) centered on the lower northwest corner of the spawner. This is easily accomplished by expanding the dungeon to 9×9, lowering the floor two blocks below the spawner, and building the killing platform so that it extends away from the spawner. When a zombie or drowned wanders outside that volume, it is no longer counted in the mob cap and the spawner keeps producing more zombies. This way it is possible to have over 100 zombies and drowned crowded into your farm.

Iron and gold farming
If you are in a situation where there isn't any way to build an iron golem farm for iron (say you are playing an island survival game and there is no village within thousands of blocks), or a gold farm for gold, you feel like you've mined out your area, and you no longer need drops from drowned, you can use a flooded dungeon farm to harvest iron and gold from the zombies. It's a slow but effective way to get iron and gold ingots. Accumulate gold faster than iron, however.

The flooded dungeon farm simply needs some minor modifications in your killing room:
 * 1) Add another large chest, to keep special enchanted items.
 * 2) Add a crafting table.
 * 3) Add a furnace.
 * 4) If you haven't done so already, dig small hole in the floor to discard unwanted items (leather, rotten flesh, plain gold items after you have enough gold, etc.)

Bring plenty of food, stock your furnace with fuel, craft a few stone swords, and do the following:
 * 1) Switch to Hard difficulty to maximize the zombie drops of gold and iron items.
 * 2) Kill the zombies as they enter the killing chamber. You can wait for them to drown but you don't have to. The zombies still drop their items whether you kill them or if they convert into drowned. However, if you see an armored zombie, let it drown, because an armored zombie requires more hits to kill.
 * 3) Periodically check the collection chest and remove any iron or gold items (and copper ingots from any drowned), and put them in your inventory.
 * 4) * If you get a sword or iron shovel, use it as a weapon but don't use it until it breaks. This lets you avoid crafting more swords to kill the zombies. You're going to smelt it into a nugget, so you may as well get some use out of it first.
 * 5) * An iron sword kills a zombie or drowned in four hits. A shovel needs seven hits.
 * 6) * Pay attention to the durability as you use these swords or shovels. When the durability bar shows that the item is nearly depleted, put it in your inventory and move on to the next weapon. Don't try to repair them. You need each worn-out iron weapon or tool to get an iron nugget.
 * 7) When your inventory is full, use the furnace to smelt your iron or gold items (especially the worn-out ones you used as weapons) into nuggets.
 * 8) Use the crafting table to craft the nuggets into ingots.
 * 9) Remove non-smeltable remaining items from your collection chest and throw them down the hole.
 * 10) Repeat.

You can collect gold ingots rather quickly this way. Iron is much slower. With luck, you can collect enough iron nuggets to make about 5 ingots per hour. It's a grind, but depending on your situation, this may be a viable option to obtain iron. As a bonus, you accumulate a lot of experience while doing this.

Survival mode build: Aerial platform
An aerial spawning platform offers a way to farm naturally-spawned drowned, which can drop tridents when killed by the player. Like the flooded dungeon above, the most basic survival-mode aerial drowned farm doesn't require exotic materials, but it requires a large quantity of common materials such as cobblestone, water, and glass. You'll also need some slabs, wooden buttons or signs to control water flow, as well as a hopper and a chest.

This farm relies on light attenuation by water to create sufficient darkness in a spawning room with flowing water to sweep the drowned into a killing area.
 * Bedrock Edition has an interesting feature in which one layer of water attenuates light by 2 levels and provides further attenuation of 1 light level per block of distance beneath the water layer. Therefore, a single layer of water on a glass roof attenuates full sunlight to zero 13 blocks below the water. This farm was built and tested $$ using this feature as an alternative, but the general purpose farm described works in Java Edition also.
 * Efficiency: The point of this tutorial is to describe a basic survival-build farm that produces tridents and nautilus shells. It can be made more efficient by contriving to put a turtle egg or villager in the center of the spawning platform to draw the drowned to their death.

Components
The main components of an aerial drowned farm are (from lowest to highest elevation):
 * A location, preferably in deep ocean, preferably at least 50 blocks away from land
 * A tower to climb, from which to build structures at high altitudes
 * A killing platform
 * A drop shaft
 * A drop platform; a small water platform some distance (like 20 blocks) above the killing platform to funnel drowned to fall into the drop shaft and onto the killing platform
 * A spawning platform at least 24 blocks above the killing platform

Preparation
Before starting, you need to collect:
 * Several full stacks of cobblestone
 * If you can get a lava bucket, you can make a cobblestone farm to get an endless supply
 * You need cobblestone blocks not only for building, but for making stone pickaxes to harvest cobblestone from the farm, and to make stone stairs for getting around the top of the farm, as well as stone slabs to prevent mobs from spawning on exposed horizontal surfaces
 * 4 to 5 full stacks of glass blocks; this may be the hardest material to collect without a desert nearby
 * A couple stacks of ladders or scaffolding for climbing back up your farm if you fall during construction.
 * A hopper (optional, but makes collecting loot easier)
 * A chest (preferably two for a double chest)
 * A handful of buttons or signs to control water flow
 * A stack of slabs
 * Two water buckets
 * At least 2 or 3 torches

Building from the bottom up

 * Climbing tower

The climbing tower is your access to the killing platform in the sky. In survival mode, building over the ocean offers safety in falling, unlike building over land. If you fall, you just have the inconvenience of climbing back up.

The most efficient way to start the tower over the ocean is to row a boat out to a deep spot with kelp growing near the water surface, allowing you to build from the top of the kelp without needing to build your tower all the way from the ocean floor, and without needing to swim. You can also put a lily pad on the water to start building from. Or, with a bit more materials and time, you can build a sea-level path from your land base out to your build location, and start building a tower out of any material, as high as you need. If you forget some materials, simply jump into the ocean and replenish. You can build a ladder up one side as you build the tower, or if you have enough material and time on your hands, your tower can be a staircase.


 * Killing platform

The first platform you build from this tower is the killing platform, and this is where you wait for the drowned to fall from above, so the minimum altitude must be out of the spawning range to the ocean floor or nearby land.

$$, mobs spawn in the range of 24-44 blocks from the player. $$, mobs spawn in the range of 24-128 blocks from the player. Building over deep ocean far from land allows for somewhat lower altitude. The killing platform where you wait for the drowned must be more than the maximum spawning range from any possible spawning location on land or in the ocean.

The basic killing platform has:
 * enough space for you to move around
 * a chest
 * a landing block onto which the drowned fall; if this is a hopper, it feeds into the chest
 * a half-block space between the top of the landing block and the bottom of the drop shaft above it; the half-block of space lets you attack while preventing any baby drowned from escaping.
 * one or two torches to keep the platform lit, to prevent mobs spawning on it while you're away


 * Drop shaft

The drop shaft is a vertical tunnel through which mobs fall onto the killing platform. The walls of the shaft need not be solid for the whole distance, it's enough to close off the sides of the shaft and leave 6 blocks of space open in the front, if you want to view the drowned falling. Drowned can drift while falling, so an open drop with no walls might prevent the drowned from falling onto the killing platform at the bottom.

The shaft doesn't have to be tall, but if you want to kill the drowned with one hit from your sword, ideally the drowned should fall 21 blocks before landing on the hopper in your killing platform. Make it too tall, and the drowned die from the fall, and you don't get any experience or tridents or other drops. If you make the shaft shorter, you just have to hit the drowned more times to kill them &mdash; up to four hits with a stone sword, which is also required from the flooded dungeon farm described above. One hit with a stone sword is sufficient to kill a mob that fell 21 blocks.

This is needed only if you are using the glass-roof darkness mechanic in Bedrock Edition.
 * Drop platform (if using Bedrock Edition glass roof)

This is a small room at the top of the drop shaft. The drowned fall into this room from the spawning platform above it. The purpose of this room is to create a measured distance for the drowned to fall, because the spawning platform is by necessity a lethal fall distance higher than the killing platform, and you don't want the drowned to die except by your own hand! So you must build a small platform covered with flowing water for the drowned to fall into safely, and be swept by the water into a 1×1 hole in the corner of the room, which is the top of your drop shaft.

One water source block diagonally across from the exit hole is sufficient. Place a wooden button or a sign on the wall just above the hole to keep the water from flowing into it.


 * Spawning platform

The water in the spawning platform must be at least 24 blocks from the killing platform, because mobs don't spawn nearer than 24 blocks from the player. Make it as large as you want. it can be as small as 2×2 but larger means more drowned. Flowing water is used to sweep mobs into a hole. A small spawning room can sweep the mobs to a hole in the side or corner of the room. A large spawning room, say with at least a 16×16 surface, would have water sweeping the mobs into a hole in the center.

(If you make the center hole 3×3, you can float a stone block above the hole with a turtle egg on it to attract the drowned to the hole, with trap doors around to make the drowned think there's a path to the egg. The turtle egg doesn't hatch when not on sand. However, getting a turtle egg requires a tool enchanted with Silk Touch, which may not be readily available to a player in survival mode. The farm still works without the turtle egg although the drowned are slower about falling through.)

Your spawning platform should be completely covered with flowing water to sweep the drowned into the drop platform room below. Ideally the water should just reach the edge of the hole, but if water flows into the hole, you can stop the flow with a sign or button. Your drop room below the spawn chamber should be configured so that drowned are swept into the drop shaft.


 * Spawning room

The walls around the spawning platform should be tall enough to provide sufficient darkness on the spawning floor. In Bedrock Edition, it should be 8 or 9 blocks tall to guarantee sufficient darkness on the floor after the transparent roof is in place. In Java Edition, you will need the wall to be at least 9 blocks high to accommodate a layer of signs and several layers of water (17 layers of water guarantees total darkness on the spawn surface). Place slabs on the top of the wall to prevent mobs from spawning on it.

One layer above the flowing water on the spawn platform floor, you need a layer of signs covering the area, to hold up columns of water above.

On top of the signs, place 18 or more layers of water to make the light level zero at the bottom. Drowned spawn in this water and drop through the signs onto the spawn platform. The deeper you make it, the more opportunities drowned have to spawn, especially in the daytime during which the top 17 layers of water are not dark enough for spawning drowned.



This alternative requires a layer of glass blocks and only one layer of water, instead of several layers of water. It works only in Bedrock Edition.
 * Alternative spawning room (Bedrock Edition only)

Make the ceiling completely from glass blocks, with at least six blocks between the floor and bottom of the glass. 1 block of stone wall (excluding the slabs on the top edge of the wall) should extend above the top of the glass, to form a shallow pool that you must fill completely with water source blocks (no flowing water). You can build a temporary infinite water source off to the side to work with as you fill the pool.

Using a glass-bottomed pool for the ceiling takes advantage of the fact that drowned spawn under water but not on transparent surfaces, so they end up spawning on the platform under the glass. The water attenuates the sky light by 2, and each block of space under the glass causes further attenuation. One needs at 13 blocks of space (including the glass) under the water for the light level to be zero on the platform to let drowned spawn during the daytime. Drowned also cannot spawn on bottom slabs, but using bottom slabs instead of glass for the bottom of the pool makes the farm inoperable. The bottom of the pool must be glass.

Operation
The farm becomes operational as soon as the glass-bottomed pool is filled and you descend to the killing platform. Whack at the drowned legs with your sword (or your fist), and start collecting loot and experience. Fish also spawn in this farm and mostly swim upstream avoiding the fall, but once in a while they fall through and die. This does not affect drowned spawning, but expect to see an occasional raw cod or salmon appear in your chest.

To increase the farm performance, stand on your killing platform and clear all the hostile mobs from the world by temporarily switching the game to peaceful difficulty and then back. Then the only available location where mobs can spawn is your spawning platform. Switching the difficulty to "hard" yields better loot in the collection chest.

Improvements
The aerial farm described here is slow, although it does produce tridents and nautilus shells. This is the most basic farm, needing only basic materials that are readily available in survival mode.

One reason for the slow yield is due to the mob cap. For example, $$, only five naturally spawned drowned can exist at any given time. The drowned try to resist the water flow in the spawn platform; therefore they spend much time facing upstream inside the platform before eventually falling through the hole.

To speed things up, the drowned need to face the hole. One way to do accomplish this is to find a turtle egg. Unfortunately, once you find a turtle egg, retrieving it requires a pickaxe enchanted with Silk Touch, which may not be available easily in survival. If you can get a turtle egg, your spawning platform should have a 3×3 hole in the center with a block suspended in the middle, connected to the edge of the hole by trapdoors in the open position so that drowned are fooled into thinking they can pathfind to the egg to trample on it. Instead, they fall through the trapdoors. The turtle egg doesn't hatch unless it's on sand. Drowned are not automatically attracted to turtle eggs; they must happen to look in the right direction first, but once a drowned sees it and can find a path to it, the drowned goes for it and falls through the hole.

The best bait is a villager, but in a survival build, it is impractical to transport a villager high in the sky to the spawn platform. Also, if playing an island survival game with few resources, there may not be any villages available to poach. This gets into more exotic farms. The purpose of this tutorial is to teach the basics of drowned farming in survival mode.

To bypass the mob cap and dramatically increase the production rate, you can have the drowned be swept into a Nether portal, so the drowned disappear from the Overworld and drop onto a killing platform in the Nether. This works fine if you are the only player in the world, but if there are other players in the Nether, they need to be within the despawning radius of the killing platform to prevent the drowned from despawning in the Nether.

Complex variations
The basic flooded-dungeon drowned farm described in this tutorial is quick and simple to construct in survival mode. It isn't automatic, however. It requires your involvement to harvest items from the drowned. While it doesn't yield tridents (and doesn't yield nautilus shells $$), that farm is still useful for a survival-mode zombie loot farm to get experience, tools, armor, and weapons with occasional interesting enchantments, as well as other items &mdash; without needing to build a deep falling pit or a tall structure in the sky.

Drowned farms on the ocean floor are more complicated because they function similarly to a mob farm, capturing naturally-spawned drowned. First, the drowned should be attracted to one location. Once they are attracted, they need to be funneled into one area where the player can easily kill them. The attracting is often done with villager bait and the funneling is often accomplished with bubble columns.

Fancier variations
Some farms incorporate innovative ideas such as bubble-column elevators to bring items to surface level, and devices to sort items. The player can circumvent the hostile mob cap (but not the maxEntityCramming gamerule) by pushing the attracted drowned into the Nether dimension. If the Nether dimension is unusable for this purpose, then the bubble columns can transport the drowned up to the player's AFK spot, typically high in the sky.

Java Edition
A river biome converted to drowned farm:

This river biome farm uses a flying machine to place over a million water blocks quickly. The depicted method of harvesting the drowned from this farm, however, is dangerous in survival as it involves swimming after trident-throwing drowned in a crowd of other drowned.

Basic underwater farm:

Advanced river farm (fastest design):