Abstract: A method of treating lake water to remove suspended solids and to precipitate and inactivate phosphorus comprises adding aluminum hydroxide sulfate to the water in a concentration such that the pH of the water is maintained at a level of greater than 6.0 and precipitation of suspended solids and precipitation and inactivation of phosphorus occurs. This invention is advantageous in that it provides a method of removing suspended solids as well as precipitating and inactivating phosphorus in water while simultaneously preventing the solublizing of toxic amounts of aluminum into the water with subsequent detrimental effects to aquatic life.