Greenwood Lake is an interstate lake between the states of New Jersey (Passaic County) and New York (Orange County). As early as 2004, the EPA's Northeast Water Region identified Greenwood Lake as being impaired for designated uses (bathing/recreation) because of high phosphorus levels. The most significant sources of phosphorus are runoff from land surfaces, failing/inadequate on-site septic systems and internal load from the sediment (NJDEP, 2004; NJDEC, 2005). Upon request of the Greenwood Lake Environmental Commission, Passaic River Institute at Montclair State University assessed the water quality of the lake. A total of 11 sampling sites were selected throughout the lake. Parameters including dissolved oxygen, pH, salinity, conductivity, transparency, total phosphorus in sediment, total phosphorus in water, orthophosphate, zooplankton, phytoplankton, macroinvertebrates, plants, and total coliform, were studied to assess the condition of the lake.
The average concentration of total phosphorus (TP) for sediment was 3.97 ± 3.38 g of phosphorus (P)/Kg of dry sediment (g/Kg), ranging from 1.48 to 13.01 g of P/Kg with the highest TP concentration representing the deepest sampling site in the center of the lake. Water TP concentrations produced a mean of 0.15 ± 0.10 ppm in a range between 0.05 and 0.41 ppm. All this confirmed that the lake is indeed a nutrient rich waterbody and that strategies to control P loading are imperative to improve water quality. Among the algal community, 86% was represented by cyanobacteria with the potential to produce cyanotoxins. Analysis of the toxin content revealed the presence of microcystin.