When a river floods and gets silted up and brown why dont fishes gills get silted up ?

Question

and how do they feed amongst the murky mud if the flood lasts for weeks ?

Answer 1

They do get "silted up" and they don't feed.  Fish that require cold, fresh, running water in streams and rivers, like Trout and Salmon, have a real problem with their water when it's polluted up with mud and silt.

That is not the biggest problem with murky water though.  When "clear-cut" logging is done by the big lumber companies, the "real" problem is caused by two things:   The land they have cleared of all trees and brush.  And, the roads they have cleared through the forest to get to these places to lumber.  These two areas cause very bad erosion when it rains, and the mud and dirt from this erosion washes down the hills and into the rivers, etc.  This is when the most severe problem occurs.  The mud and silt washing down from these areas gets into the water and fills up the small spaces between and among the river rocks and pebbles lying on the bottom.  Since these spaces are filled up, there is no place for the fish to lay their eggs, since their eggs "need" to lie in these spaces.  The eggs need to be there or predators will pick them all off and there will be no new fish.  The adult females "know" this, and therefore will not lay their eggs.  And, as you can imagine, this creates great problems with reproduction and the maintainance of the health of the river ecosystem.

Nature "will" take care of itself if man will just leave it alone, or at least, find alternatives to the way he does things.