Pond water turns green when there is excess algae. Algae need sunlight and nutrients to grow. While you can’t do much to control how much sunlight reaches a pond, you can manage the amount of nutrients in the water. Do not use fertilizer within 10 feet of the pond. Do not mow right up to the edge of the pond—instead maintain a buffer of grasses and flowers around it. Keep livestock and pet waste away from the pond. If you have an aerator, make sure that it is properly maintained.
Click HERE for more pond management information from the Illinois Department of Natural Resources.