Phosphorus Impacts on Lakes, Rivers

Excess phosphorus in lakes causes algae blooms and excessive weed growth (a process called eutrophication), resulting in fish kills, decreased water quality and decreased water recreation enjoyment. Phosphorus is a pollution concern in lakes, rivers and streams.

How Phosphorus Enters Lakes

In urban environments, lawn clippings and tree leaves left in the streets and gutters wash down storm sewers into surface waters; these contain phosphorus. Other sources of phosphorus may come from soil eroding into water. In lakeshore areas, bare soil washes into the water, adding phosphorus to the lake. Fertilizers applied to lawns, gardens, farm fields and pastures along lake shore can cause run-off into the water if excess is applied, or applied just before a heavy rain. Failed septic systems around lakes can discharge phosphorus and bacteria directly into the lake.

Phosphorus is normally bound to soil particles and then used by plants. Problems occur when the fertilizer is washed off the plants before it enters the soil, when soils erode into the water, or when there is too much in the soil. Some areas of the country are naturally high in soil phosphorus.

What to Do to Reduce Phosphorus in Lakes and Rivers

• Do not throw leaves, grass clippings, pet waste, other organic debris into the street or driveway. Runoff carries these through storm sewers, directly to lakes and rivers.
• Build a rain garden to filter run-off from roofs, driveways, streets. This allows the phosphorus to be bound to the soil so it does not reach surface waters
• Some states require phosphorus-free fertilizer with a couple of exceptions; know the laws of the state.
• Never apply fertilizer to frozen ground.
• Water your lawn after fertilizing, but don’t apply if heavy rains are predicted.
• Sweep up fertilizer that is spilled or inadvertently applied to hard surface areas, do not hose it away.
• Sweep curbs and gutters to reduce nutrients and other organic material carried in runoff water.
• Aerate lawns with excess thatch problems to encourage better water infiltration, thereby reducing runoff.
• Lakeshore owners should leave an un-mowed buffer strip between the lawn and lake, or a strip of natural vegetation along the shoreline. Mowing right to the shoreline gives more opportunities for phosphorus to enter the water.
• If on a septic system, have it inspected and pumped regularly to make sure it is working properly.
• Do not burn brush or leaves on a slope leading to surface waters. Ash washing into the lake adds nutrients.
• Use non-phosphate laundry and dishwasher detergents.

Phosphorus and Algae Blooms

Algae are single-celled organisms that support the entire food chain above them. Algae are necessary to a healthy lake, but too many algae can be difficult. According to University of Minnesota Extension Educator Barb Liukkonen, ‚”Phosphorus is the nutrient of most concern in Minnesota because the growth of aquatic plants in our lakes is usually controlled by how much phosphorus is available. Under the right conditions, a single pound of phosphorus can lead to 500 pounds of algae!”

Help Limit Phosphorus Access to Lakes

Following these tips will help protect the quality of lakes and rivers, enhancing water quality, water recreation and fish, animal and plant life.