Y’arg, pirates.
Giant toad.
Giant fey toad.
Dire crocodile.
Devilfish.
River drake.
River giant.
Hippopotamus.
Behemoth hippopotamus.
Giant leech.
Freshwater merrow.
Water naga.
Anaconda.
Nixies and Nyads.
It’s a relatively calm day, the sun is bright, a few clouds dot the sky as your PCs sail peacefully down river. Suddenly there’s a shout, and looking over, they see another ship, half sunk and scuttled on the river bed. There’s a commotion in the water around the ship, like a churning and boiling mass. As you near, the churning leaves the scuttled ship and heads your way. It suddenly becomes clear, it’s a swarm of rats! Prepare to be boarded!
Do any of them have any influence on the sailing itself? You could have some encounter where they have to use skill checks, like going through rapids and/or taking boat damage, etc. If not, @djdust has suggested some great ideas for creatures to fight.
