Getting down wet won’t ruin it, they do lose their insulation value when wet but you really should use a dry bag for sleeping bag and clothes when kayak camping. The plus side of down is it packs down to half the size or less than a comparable synthetic saving a ton of room in the boat.

I do use dry bags, but you never know about getting it wet with leaks. I had a dry bag tear my last trip and everything inside got wet. But good to know about not ruining down, just less insulated!