The Water Tram is a fast travel creation which consists of streams of water flowing in the direction you wish to travel. Water trams are usually created using water, a boat, and pressure plates. Since water flows in both directions, the pressure plates are necessary to break the water up into streams flowing only in the direction you wish to travel. Since the introduction of ice travel, this method has become somewhat obsolete, as boats travel much faster on ice than in currents.
To build the tram, first place two lines to contain the water with at least two blocks of space between them. Next, at the beginning of the lines, place buckets of water stretching between the lines. At the end of the flow of water or somewhere before, place pressure plates to prevent a backwards flow. Right after the pressure plates, place more water and repeat until it becomes as long as wanted. Refer to the photo if you get confused. Making two parallel trams in opposite directions can allow easy two-way transportation. The pressure plates can be connected to redstone circuitry and act as motion sensors.
Pressure plate frequency
The ideal frequency of pressure plates is unknown. The following paragraph contains some outdated information which may still be relevant. Note that boats are much more durable now and will not easily break when hitting a pressure plate or other block.
The best setup is to have 5 water blocks per section (1 source + 4 flowing); any more than that and your boat will hit the side of a pressure plate and break. It's also the fastest, traveling at about 7.7 blocks per second (192 blocks in 25 seconds) - 35% faster than sprinting, and without the hunger drain. If signs are used instead of pressure plates, sections can have up to 7 water blocks, but this does not significantly increase speed, and requires more resources. Making the sides of the road out of pressure plates as well is recommended; boats will break if they hit full or half blocks.
This video shows the construction of a water tram, but it is very likely outdated, because it was made in 2010.