I can empty the fish traps under water from land without hydration problems as long as i don't use an empty hand. Try it with something in your hand.I have noticed two things concerning the polluted seas questline:
1. The fishing quest states that you need a male and a female cod. I have pulled out quite some fish, yet there was no cod. Nevertheless the quest showed up as solved ... is that intentional?
2. The fishtrap you get as a quest reward has a nasty "feature". When I click on the trap after it is place and do not the spot of the inventory but on the frame it looks like it is replacing the thirst. But this only last for a few second before your hydration level goes down straight to zero, empties your camelpack and gives you dehydration. Is that a bug in the mod or some evil little surpise being set up?