If a tsunami gets into a net that's imprisoning a bunch of insects, the insects are going to get all muddy. The net gets dragged along with the tsunami water and the insects can't escape, so they just get covered in the yucky stuff.
Unfortunately for the insects, these muddy conditions have created the perfect habitat for ducks (だく). And muddy insects already imprisoned in a muddy net is a duck's favorite treat!
Currently there are no similar looking kanji which exist in the WaniKani learning system