I tried to cross a narrow strait, but when my character moves onto the ramp tile indicating deeper water, the game stops responding to keyboard input. Cannot move, or bring up any menus, the animation still goes on and so does time, because my adventurer quickly gets drowsy, hungry and thirsty while being stuck. Also, his speed rises as if he was getting lots of swimming xp while seemingly immobile. DF.exe uses all available processing power while I'm stuck and soon the night falls and I get encased in ice (entered the water at dawn, around 20 tiles back East). The only way to get through the ramp tile is to move carefully to (above/air), fall down to the bottom behind the ramp and swim on the bottom level, which eventually leads to drowning. Trying to resurface at any point results in the same stuck situation.
Moving to a different location and trying to swim in the sea yields the same results.