"This divide runs from Cape Prince of Wales in western Alaska, through the Rocky Mountains of western Canada and the continental United States, then through the Sierra Madre Occidenal mountains in Mexico, through central America and along the Andes Mountains or South America"
Flooding can affect rivers because river flooding causes things to be picked up from the streets and pulled back into the water. So It affects the water quality and if anything dangerous to the fish and water life gets in the water it will mess up their life system. Hope this helped a little bit. :)
The answer to your question is DRIED PLANT MATTER ❤️