Phosphorus is a chemical element that is highly reactive and is never found as a free element on Earth. We use the vast majority of phosphorus is in fertilizers; other applications include detergents, pesticides, and nerve agents. None of these things should be in our lake water.
Phosphorus gets into the lake through erosion and sedimentation. Clay contains higher amounts of phosphorus than other soil types. Unfortunately clay particles are easily carried by stormwater runoff. The heavier and less phosphorus rich soil particles like sand and gravel tend to settle out more quickly.
Low phosphorus levels are critical to lake health. Lake algae populations are typically limited by phosphorus concentrations in the water. You add fertilizer (key ingredient is phosphorus) to make your lawn grow. When you add phosphorus to a lake more algae grows. Just like plants, algae need sunlight so they grow in the upper, sunlit water. As their populations increase, water clarity diminishes.
Algae growth is a vicious cycle. The algae die after a few weeks and the dead growth falls to the bottom where it decomposes. Dead algae are decomposed by bacteria in the bottom waters of the lake. This process consumes oxygen. Fish need oxygen in the lake so as the algae thrives the fish diminish.
Once all of the available oxygen in the bottom of a lake is used up a complex chemical reaction begins. This reaction releases phosphorus from the sediment in a process called internal phosphorus recycling. This stimulates more algae growth, leads to less dissolved oxygen in the bottom waters, and further offsets the lake's natural equilibrium.
You can help prevent the cycle that chokes our lake and kills our fish by:
Preventing erosion. Retain natural undergrowth and vegetation. Plant roots keep the soil in place. Use gravel or other retaining materials to prevent soil from being carried into the lake.
Do not use fertilizers around lakes or the streams that feed them. Plant fertilizers contain high amounts of phosphorus. Do not use fertilizers around lakes or the streams that feed them.
Make sure that you are not putting detergents into the water. Use only soaps meant for lake use when cleaning near the water. Make sure that all septic and greywater systems are functioning properly.
Oxygen is for fish, not algae!