Ensuring that our lakes and other natural water sources are clean is an important factor to the quality of our drinking water. Plus, when lakes get too contaminated with excess algae, they are no longer available for public recreational use and sit unused due to public safety concerns. Over time, unhealthy lakes will become murky and smelly because of too much planktonic algae growth. A lake with too much algae is the sign of an unhealthy lake because the more algae a lake has, the less light can penetrate to the bottom of the lake. This means that submersed plants that normally thrive at the bottom of lakes cannot grow and aquatic life will suffer.

Since high levels of phosphorous in a lake leads to high levels of algae, algae can be reduced by removing its source of growth. While phosphorous is vital for plant growth, too much phosphorous in a lake is not healthy. Introducing aluminum sulfate into a lake successfully reduces the levels of phosphorous and thus the levels of algae.

Aluminum sulfate appears as a white crystalline solid in its purest form and does a great job of cleaning lakes. In order for alum to clean lake water, it must be introduced into the lake with a second chemical called sodium aluminate. By itself, aluminum sulfate would make a lake so acidic that aquatic life in the lake would die. When sodium aluminate is introduced into the lake with aluminum sulfate, it acts as a buffer to the alum and maintains a neutral pH in the lake. Typically, the two chemicals are pumped from a large temporary tank onto a boat that has two separate tanks on board. Then the boat will slowly apply both chemicals to the lake, refilling the tanks as necessary.

Once the chemicals have been added to the water, a flaky white mass called floc will be formed. This floc chemically binds the phosphorous, which sinks to the bottom of the lake and effectively removes the opportunity for algae to grow. With less algae in the water, light can penetrate deeper into the lake and allow plants to grow at the lake bottom, which improves the overall health of the lake.

Ironically, while aluminum sulfate is a safe means of cleaning a lake, it is a hazardous material that can cause irritating side effects to humans. The aluminum sulfate undergoes a chemical reaction with water that forms sulfuric acid, which is responsible for symptoms that vary depending on how it comes into contact with people. When inhaled, it is known to cause irritation to the respiratory tract; when ingested, it irritates the gastrointestinal tract; and when it touches the skin or eyes, it causes redness and pain.

Nevertheless, scientists have found that using alum to clean lake water poses little or no risk to humans, fish or other wildlife. When applied properly to lakes, it appears that the benefits of a clean and healthy lake far outweigh any potential side-effects of using alum to clean lake water.