II. Water Quality and Phosphorous

Phosphorous and where it comes from

Although several pollutants are a concern to our water quality and the NYC reservoirs, phosphorus is of particular concern. Both phosphorous and nitrogen are naturally occurring nutrients essential for plant growth. However, there is a much greater supply of nitrogen in the environment. Phosphorus, being the nutrient least available and the easiest to control, is considered the limiting nutrient in algae and plant growth. Phosphorous comes from many sources. Soils, weathered minerals and rock, decomposing organic material, car exhaust, failed septic systems and atmospheric deposition all contribute to the amount of phosphorus in the watershed.

Croton Reservoir System

The New York City Water Supply System includes a watershed of 1,969 square miles across eight counties north and west of the City: Westchester, Putnam and Dutchess on the east side of the Hudson River and Delaware, Greene, Schoharie, Sullivan and Ulster in the Catskill Mountains, west of the Hudson. The watershed provides drinking water to about half the state population including approximately 1 million people in the upstate communities, 8 million New York City residents, and hundreds of thousands of commuters and tourists. The system delivers some 1.3 bullion gallons of water per day. There are also thousands of private and public wells within the City's watershed.

There are four reservoirs in the Croton system whose watershed extend into Patterson; the Bog Brook, the Diverting, the East Branch and the Middle Branch. In fact, one hundred percent of Patterson's approximately 21,000 acres or 32 square miles lie within one of these four reservoir watersheds. The reservoirs for these watersheds are all located in the Town of Southeast. The largest of these watersheds is the East Branch Reservoir Watershed which comprises approximately 91% of Patterson. The other three watersheds are the Bog Brook, the Diverting and the Middle Branch Reservoir Watersheds, which together comprise the remaining 9% percent of the Town of Patterson.


Total Maximum Daily Loads (TMDLs) is a method of assessing compliance with water quality standards based on an established water quality guidance value. It establishes allowable loadings for pollutants which can then be allocated among the various pollutant sources such as wastewater treatment plants, forested areas or agricultural lands. A TMDL is the sum of waste load allocations (WLA) for point sources, such as wastewater treatment plants, and load allocations (LA) for nonpoint sources, such as stormwater runoff. In addition a margin of safety (MOS) is included to account for the relationship between the uncertainty between the pollutant loads and the quality of the receiving water body. Although TMDLs can be calculated for any given pollutant of concern, it has been calculated for phosphorus only, since phosphorus is the limiting nutrient and therefore the pollutant of greatest concern.

In reports released by the NYC DEP and NYS DEC, the East Branch, the Diverting and the Middle Branch are all receiving more phosphorous. To maintain healthy lakes and reservoirs, and to comply with the TMDLs, the existing amounts of phosphorous from non-point sources in our watershed must be reduced.

Best Management Practices

Best Management Practices (BMPs) are methods, measures or practices to prevent or reduce water pollution. They can be divided into two types: structural BMPs, which are constructed practices such as catch basins, grass swales or detention ponds, and cultural BMPs, which are methods, measures or practices that affect or change an individual's behavior, such as proper usage and disposal of household products and good housekeeping.

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