Avoid transporting species. When you move your boat from one area to another, make sure that you do not transport water with you, since it can carry destructive non-native plants and animals. Clean plants and algae from the boat before moving it. Use a holding tank for human waste and empty it at a designated facility. Be a watchdog.
Boaters are in a unique position to keep an eye on the river.
If you see things that are wrong, from garbage to eroded banks to pollution from pipes, do what you can to investigate or solve the problem. Most of these projects are great for church or office groups, or for student service. Plant a tree. Participate in plantings in cities, local parks and riverbanks. Trees and shrubs always help filter water and clean the air.