How does the water effect animal life in the river?

Water affects marine [sea animal] and even land animals drinking from it in different ways. Since this is in the category 'Pollution', I suppose you want to know what pollution does to animal life. Marine life is affected by acid rain, which is caused by major excretions of Sulfur Dioxide and Nitrus Oxide, as well as natural sources, such as decaying vegetation and volcanos. Acid Rain, when shed into the rivers and lakes that fish and other animals inhabit, can raise the acid amounts in the water, making it toxic for the animals.

Now if you mean the dumping of trash into the water, that's a different side. Imagine living in a room of trash and harmful chemicals, breathing it all in with no way to get out. It's the same with marine enviornments. Fish breathe it in and die. (Ever seen one of those Cartoons where a character tips over a garbage can or stinks so bad, when they/the garbage hits the water, fish come up to the surface with X's on their eyes? Its the same with pollution.)

I hope that answers your question. I simplified it the best I could.