The main ways are...
1..stop putting the chemical wastes in rivers without proper treatment of water.
2..we gotta stop throwing our house wastes near river or in river.
3.don't let bad micro organism to exploit the water..
4..the main one is just try to be aware and responsible for your environment..think that its your property...if you'll apply 4 point on yourself then you will also contribute in saving rivers
hope it helped .
please mark it as brainliest.