Phosphorus is a nutrient that can be found almost everywhere. Foods high in phosphorus, like meats, beans, and nuts, help build strong bones and teeth. We need phosphorus in our bodies. Likewise, plants need phosphorus too. When plants consume phosphorus, they grow lush with strong roots. Therefore, farmers and homeowners often apply phosphorus-containing fertilizers to the soil. As plants grow roots in the soil, they start to use the phosphorus, helping them grow tall. But, sometimes there is more phosphorus in the soil than the plant really needs. The excess phosphorus remains in the soil, not really being needed or used by the plant.

Too much phosphorus becomes a bad thing. Excess phosphorus in the soil can pollute nearby waterbodies, such as our lakes and streams, through soil erosion. Because phosphorous easily binds to soil particles, wherever the particle goes, the phosphorus goes with it. Think of the phosphorus getting a piggy-back ride on the soil particle.

Wind, heavy rain, the plowing of a tractor can all make the soil loose, exposing the soil particle, and causing soil erosion. In soil erosion, the particle is stripped from the landscape and tumbles downhill, following the flow of the rainwater on the earth’s surface. If a storm is strong enough, the water will carry the soil particle all the way to a nearby lake, where the particle sinks, bringing phosphorus to the lake bottom.

Phosphorus in a lake will do what it normally does: it fuels growth. Algae, a diverse group of aquatic organisms, can easily use the phosphorus, and they are the first to grow rapidly. Algae thrive in nutrient-rich environments. Algae grow abundantly, reproduce rapidly, and outcompete aquatic plants. Soon, a green film of algae covers the lake, preventing sunlight from reaching the lake bottom. This bloom of algae will not only be smelly and visually unpleasant, but it can, depending upon the type of algae, be toxic to humans. Blue-green algae, for example, release toxins that can make people sick if they come into contact with the algae while swimming or boating.

During an algae bloom, aquatic plants on the lake bottom no longer receive the sunlight or the nutrients they need to grow. They start to die and decay through decomposition, a process that requires oxygen. Without oxygen in the water, the fish too suffer, suffocate, and die. They float to the surface, belly-up.

Excess phosphorus is an example of nonpoint source water pollution. The phosphorus cannot be traced to a single pipe or source, but rather, the pollutant comes from all over the landscape. In nonpoint source water pollution, the pollutants come from diffuse sources on land and eventually make their way into our waterbodies where they offset the natural ecosystem. Nonpoint source water pollution impacts recreational activities, such as fishing, boating, and swimming. In severe cases, the pollution can even impact human health. To restore the waterbody can often take years, and may require costly clean-up actions, such as dredging the lake bottom to remove soil particles or adding aluminum sulfate to chemically bind with excess phosphorus. It is better to prevent the nonpoint source of pollution from ever entering our waters.