This pack features river tiles, some open water tiles, including a monastery, and a boat with a sea monster emerging. You can find waterfalls, river corners, islands, forks, and river exit into a lake/sea/ocean.
These tiles are meant to work with the base pack available, as you can see in this map provided. It also works, with all other base-variant addons, you can get those here as well!
As always the tiles are available both in _pack file for Dungeondraft, and in PNG files for image editing softwares.