Channels are used to direct the flow of fluids (namely, water and magma). When fluid enters a channel, from either a floodgate or a direct connection to a river, it will spread into every adjacent channel around it in all directions.
Channels are built using the- command and can be resized to up to 10x10 using the / keys.
Channels can be set to ponds by using thekey on them while they are not full of water, or get assigned to other channels specifically in the event of overlap. Unless you have a floodgate in place, it is impossible to get water back out of a channel.
While it is possible to divert water from the outside river, it should be noted that this is probably a bug as water should not be able to flow uphill to the mountain.
Bridges cannot be built over channels that have not yet been filled with water. Examining a channel using the 'k' key should reveal multiple "Channel" items in a single square - one is a building, while the other is a terrain tile. To correct this problem, build a small channel adjacent to the first (1x1 is large enough), and cancel it using - after a miner has begun to dig it, but before he is finished. This should remove the extraneous "Channel" buildings and permit the construction of bridges.
Warning: Once dug, channels can only be removed by a cave-in. If a wall tile from a cave-in falls on a channel, that channel tile will be removed.
To build a channel, you need a dwarf with the mining labor. It is common to create channels to direct water towards the cave entrance, for defense, or further into the mountain, for defense or farming far inside the mountain.
Dwarves will often suspend construction of a channel that looks like this:
▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ __●__●__●____●____●_ ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
This is typically caused because some task is assigned to one of those stones, usually a hauling task. The task must be cleared through one means or another before the construction can finish. Another situation in which channels may be suspended during construction is when building a long channel that spans an entire hallway. If sections of the channel to either side are not yet fully constructed, dwarves will be unable to remove obstructions from the central section until at least one side is finished. Once a channel has been constructed, rocks and other objects on top of the channel will not disrupt the flow of fluid, or prevent the channel from filling.
 Game mechanics
- Once a channel is built, it counts as a building and can be interacted with using the command (for example, to designate it as a pond).
- Once a channel is filled with water, it ceases to be a building (and can no longer be designated as a pond) and it becomes possible to build bridges over it, even if the channel is subsequently drained. This does not happen when the channel is filled with magma.
- A channel filled with water blocks movement to creatures that do not fly or swim. Channels filled with magma block movement to all creatures that are not immune to fire.
- Cave river floods (the natural ones, as opposed to those caused by quality craftsdwarfship and floodgates) treat channels as normal open floor. Channels will not stop natural floods, and natural floods will not cause the channels to fill with water.
- An empty channel can be filled by connecting it directly to a river. In this case, the entire length of channel will be filled. If magma is subsequently introduced into the channel, it will dry up and will not refill with water once the magma is removed.
- An empty channel can also be filled by connecting it to a floodgate that is adjacent to a river. In this case, the entire length of channel will be filled when the floodgate is opened. When the floodgate is closed, the channel will drain.
- An empty channel can also be filled by an artifical flood. In this case, the entire length of channel will be filled.
- A full channel will not release water into a non-channel square.
- To get a normal open area flooded, a floodgate has to link a channel to the open area.
- Because channels will not release water to normal open areas, you can use a channel to stop artificial floods.
A pond can be created by digging a channel and setting it to "currently a pond" (as opposed to "currently a channel"). After setting a channel to become a pond, your dwarves will begin filling the pond with water using buckets (this is a job that may be performed by any dwarf, including nobles). Live fish can be assigned to a filled pond, where they will swim around and look pretty, although they will not reproduce, so dwarf-made ponds cannot be used for fishing.
Ponds increase the value of the room. Ponds with fish in them increase the value of the room even more.
The water in ponds will slowly evaporate, so they must be refilled periodically.
Pond water is considered shallow so dwarves (and other creatures) can wander freely in the water.
Once a channel has been filled with water from a river, it can no longer be designated as a pond.