One idea could be to be able to put a domestic goose in a filled ditch and can move between adjacent ditch tiles, so they can swim like in a pond. This would mean something a little cool for towns with large water features. Throw in a slice of bread or corn kernels and they could leave an egg on the nearest free land tile. In addition you could change the behavior of a goose to follow someone in the water if they have bread or kernels.
You can also add a raft that can move ditch tiles by using a saw on a pier/bridge or something like that. An alternative idea could use a log canoe.