Phosphorus is a nutrient essential for plant growth. It is found in lawn fertilizers, manure, as well as human and other animal waste. Too much phosphorus in water causes algal blooms and excessive aquatic plant growth. These plants and the water quality problems that occur when they decompose can harm fish and other organisms and limit our use and enjoyment of the Lake.

Phosphorus levels are elevated in many parts of Lake Champlain, such as Missisquoi Bay, St. Albans Bay and the South Lake. Nuisance algal conditions exist nearly half of the time in these areas. Blue-green algae has become problematic during the summer in Missisquoi Bay and other northern parts of the Lake. An agreement has been signed between Vermont and Quebec for reducing phosphorus to Missisquoi Bay. Visit the Lake Champlain Basin Atlas for more about phosphorus levels, as well as maps and charts.

As a result of reduction efforts, now only about 10% of the phosphorus in the Lake comes from point sources, such as wastewater treatment and industrial discharges. Runoff from roads and developed areas, and from lawns, farmlands, and other rural areas (called nonpoint sources) contribute 90% of the phosphorus.

A 2007 report for the Lake Champlain Basin Program, estimated that 46% of the nonpoint source phosphorus load is from urban land uses and about 38% is from agricultural land (using 2001 satellite imagery and the loading method of analysis). Urban land included all roads, cities, suburbs, lawns, and large-lot buildings. Although these developed areas are estimated to contribute the most phosphorus basin-wide, some sub-watersheds still have more runoff from agricultural land. For example, over 70% of the runoff from the Missisquoi watershed is estimated to be from agricultural use. The full report is available on the publications page. Go to the Lake Champlain Atlas for a map of estimated loading by sub-watershed.

Citizens can help reduce phosphorus by switching to phosphorus-free lawn fertilizer and phosphorus-free automatic dishwasher detergent. Visit the Save the Lake Tips page for more ideas on how you can help.

Phosphorus reduction efforts have begun to show some promising results in the Basin. The LCBP has been funding water quality monitoring for phosphorus and other indicators since 1992. Data gathered between 1990 and 2004 show no significant positive or negative trends in most segments of the Lake (except for Mallet’s Bay, St. Albans Bay, and the Northeast Arm which are increasing, and Shelburne Bay, which is decreasing). Most segments have remained consistent in exceeding, meeting or sometimes meeting phosphorus goals. Click on the graphic, or go to the Status and Trends in Lake Champlain Phosphorus Concentrations, 1990-2004 page for more details.

Results of reduction efforts are more apparent in the Lake’s main phosphorus inputs. Of the Lake's 18 major tributaries only one (the La Platte River) is close to meeting its target phosphorus load, but seven more are showing an improving trend. Only three show a worsening trend and the remaining eight show no trend. Click on the graphic, or go to the Status and Trends of Tributary Phosphorus Loading, 1990-2004 page for more details.

The most significant reductions have been achieved by targeting point sources, mainly in the form of wastewater treatment plant upgrades, and overall the trend towards reduction is positive. Click on the graphic, or visit the Status and Trends in Wastewater Treatment Plant (WWTP) Phosphorus Discharges, 1990-2004 page for more details. However, much work over many years remains to ensure that a significant phosphorus reduction occurs in Lake Champlain.

In 2006, the LCBP began working with several partners in the watershed to encourage homeowners who use lawn fertilizer to switch to phosphorus-free fertilizers. More information about this program and the "Don't P on Your Lawn" brochure is found on the Lawn to Lake website.

• Blue-Green Algae
• Missisquoi Bay Phosphorus Agreement
• Nonpoint Source Pollution Fact Sheet
• Phosphorus-Free Automatic Dishwashing Detergents (27 KB in Adobe PDF)
• Contribution of Phosphorus from Automatic Dishwasher Detergents to Lake Champlain (Feb. 2004 paper by the Lake Champlain Committee)
• Phosphorus Pages (LCB Atlas)
• Phosphorus Reduction Strategies
• Preliminary Evaluation of Progress Toward Lake Champlain Basin Program Phosphorus Reduction Goals, June 1, 2000 (A Lake Champlain Basin Program Internal Report Prepared for the Lake Champlain Steering Committee)
• TMDL Program