Phosphorus is a naturally occurring nutrient essential for plant growth. It is found in many substances, such as lawn and garden fertilizers, animal and human waste, and automatic dishwasher 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.

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 species 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.

The plan for the Lake Champlain Basin, Opportunities for Action, lists the reduction of phosphorus as one of its highest priorities, and New York and Vermont have developed reduction targets for each Lake segment over a 20-year time frame. By the end of 2001, phosphorus loads were reduced by about 38.8 mt/yr (metric tons/year), far exceeding the five-year target of 15.8 mt/yr. However, to meet the long-term goal of the plan, existing and new pollution sources from development will need to be better managed. An agreement between Quebec and Vermont to reduce Missisquoi Bay phosphorus loading is in place, and a task force to carry out the agreement is underway.

The Lake Champlain Basin Program has been working to control both point and nonpoint sources of phosphorus. Point sources have been reduced significantly through wastewater treatment plant upgrades which help remove additional amounts of phosphorus from plant discharges.

However, over 90% of the phosphorus entering the Lake currently comes from nonpoint sources, which are often more difficult to track and reduce [2008 update to Atlas]. Numerous actions have been taken to reduce these nonpoint sources. They include nutrient and waste management on farms, streambank erosion control, and programs aimed at reducing phosphorus runoff from lawns and roads in developed areas.

Reducing phosphorus can also be done by all of us at home and work. Simple things citizens can do include reducing the use of lawn and garden fertilizers, properly disposing of pet waste, and washing cars on grass instead of pavement.

• Blue-Green Algae (LCBP website)
• Lake Champlain Phosphorus TMDL (VT DEC)
• LCBP Fact Sheet #2 - Nonpoint Source Pollution
• Opportunities for Action Plan (See Chapter 2)
• Smart Waterways (Chittenden County Stormwater Program)
• Urban Runoff Poster Series (LCBP)