blue-green algae bloom

Photo by MDDEC.

Phosphorus is a naturally occurring nutrient that is essential for plant growth. It is found in many substances, including soils, lawn and garden fertilizers, animal and human waste, and some detergents. Phosphorus in the Lake comes from both point sources, such as municipal wastewater treatment plant discharges, and nonpoint sources, such as runoff from farm fields and lawns. Phosphorus pollution is a significant threat to water quality in Lake Champlain.

When too much phosphorus gets into a body of water it can cause algal blooms and excessive growth of other aquatic plants. These plants, and the water quality problems that occur when they decompose, can harm fish and other wildlife and limit human uses of the Lake. Phosphorus also contributes to the growth of blue-green algae blooms on Lake Champlain. These blooms are a serious human health issue because they can occasionally become toxic and are poisonous if ingested in large quantities. Visit the Human Health Issues page for more information.

High levels of phosphorus are a concern in nearly all areas of the Lake. Reductions in phosphorus load have been observed in a few tributaries over the last decade, but these small improvements have not yet resulted in significant reductions of in-lake phosphorus concentrations. Wastewater treatment facilities (point sources) are generally meeting their phosphorus effluent targets, but much work remains to reduce nutrients washing off of the landscape (nonpoint sources). Until phosphorus concentrations in the Lake are closer to the established targets, algae blooms will continue to form when weather conditions are favorable for intense growth.