Some of us (thanks for @Sairdontis!) has problems in the water: Water stalling , intended?
If you swim alone or on horseback in the water, you are locked after activities such as something crafted, food consumed, exiting from the inventory of a loot chest, switching gear, using gear.
Please provide a step-by-step process of how the bug can be reproduced. The more details you provide us with the easier it will be for us to find and fix the bug:
Go find water to wash the dirt off of you
While you are there do stuff
Get locked in one place for several (from 1 to even 10) seconds
I don’t know about when you are on horse back but if you are not then equip a one handed weapon when you get stuck. This should allow you to move again.
I can’t leave the river after entering the river on horseback, the horse simply stutters endlessly trying to get out of the river. If I get off the horse, then I can swim to shore and the horse follows me just fine.