Battlefront has a new Battlefield In A Box product out. This one’s River Forks.
From the release:
Water features have played a major part in battles throughout history. Both streams and mighty rivers are natural obstacles that are sure to influence the strategy of any commander intent on victory. Battlefield in a Box provides everything you need to construct your battlefield, at all scales of gaming. Combine this set with the others from the list below to build more complex waterways.