The Mohegan Lake Improvement District was established in 1975, by joint action of the Town Boards of Yorktown and Cortlandt. Located in Northern Westchester County, New York, the Lake District manages 105-acre Lake Mohegan. The lake was formed in the last great ice age, but since 1900, has experienced cultural eutrophication. The lake has become increasingly prone to algae blooms, and local residents used copper sulfate to "manage" the lake for many years. About a mile long, the lake was also used for power boating, sail boating, swimming, fishing and ice skating. Not to mention the benefits of looking at the beautiful water and enjoying the company of hundreds of species of plants and animals.

In the 1970s, the Yorktown Town Board approved the construction of hundreds of units of multi-family housing on land near the lake, with the waste water going into several giant septic tanks. Residents who were trying to restore the lake didn't feel this was smart - and feared it would speed the destruction of this precious resource. The residents banded together to hire some great biologists - Dr. Raul Cardenas and Richard Knabel - and went to court. They won the case, and the Town was ordered to bring sewers to the area before allowing such density development.

After their years of hard work, and umpteen chicken barbecues to raise funds, residents realized they needed a more lasting organization to collect money and oversee the lake. They petitioned the Towns of Yorktown and Cortlandt, which swiftly approved the creation of the Mohegan Lake Improvement District under Article 12 of the Town Law of the State of New York.

The Lake District is roughly delineated to include all properties having "lake rights" to this private lake. It's hardly "private," however - with some 1,500 households now comprising the District. Currently the District raises about $48,000 a year in taxes (roughly $30 a household) to manage the lake. The District is managed by a group of volunteers, who meet the second Wednesday each month during much of the year.

Among the management efforts undertaken pursuant to an ambitious Ten Year Plan (adopted in 1990), are the following:

1. Upgrade and maintain the aeration system in the bottom of the lake. This puts oxygen into the water, for the benefit of the fish and other creatures, and to improve water clarity. Unfortunately, at least through the year 2002, the system had never been expanded to its full size, and the half-a-system did half-the-job.
2. Cut weeds that grow in the lake. The weed harvester is an orange pontoon boat that ambles around the lake during late May and June - the peak weed season - cutting about 1/4 ton of weeds per load. The weeds are taken to shore, where they are taken to a composting site. During recent years, some 10 to 15 tons per year are harvested. We don't harvest near the shore, because it's too shallow. We also don't try to remove all the weeds, since the weeds are a necessary part of a healthy ecosystem.
3. Stock fish. As most people who fish can attest, Lake Mohegan is a bountiful source of fish. Bass are a common sport fish, and the District has also stocked walleye pike, in an effort to restore the balance in the food web. Biological fish surveys showed us that the food web in the lake is far out of whack - with too many of the small "pan fish," like sunnies. This causes a depletion of the zooplankton - the creatures that eat algae. This management technique is known as "bio manipulation."
4. Aluminum Sulfate. The District has decided to seek a permit for the application of aluminum sulfate (alum) on an annual basis. Past experiments have shown that this safe chemical can improve water clarity without posing any adverse environmental impacts. Alum isn't a herbicide; it doesn't work by being toxic to anything. Rather, it attaches itself to the phosphorus in the water, and precipitates it down to the bottom of the lake, where it forms a sealing layer to inhibit the release of phosphorus for a long period of time. It's phosphorus which makes the algae grow, especially in late July and August when "blue green" algae takes over large areas of the lake.
5. Watershed Management. The Lake District has tried to stop the phosphorus from entering the lake, through proper watershed management. This includes tough new wetlands legislation, trying to educate people to use lake-friendly fertilizer, protecting shoreline vegetation and storm water mitigation. Some 80% of the phosphorus entering the lake comes from storm water. The Lake District also helped encourage the establishment of sewer districts around the lake, although there is now some question in the community whether this expensive system is worth the newly-projected costs.
6. Lake User Regulations. The Lake District convinced the Yorktown Town Board to ban power boats over 5 horsepower in 1991. The lake is quite shallow - a maximum depth of 18 feet and an average depth of 8.3 feet. The props of the boats were found to be stirring up the nutrient-rich sediments and contributing to the algae problem.
7. Other proposals. The Lake District has also explored dredging of the lake; use of non-pathogenic bacteria to stimulate sediment decomposition; barley straw; bio filters; new zoning restrictions; hypolimnetic withdrawal; alternative aeration systems, and many other possible management options.