Nutrients are critical for sustaining the marine ecosystem, but can be harmful to an estuary at excessive levels. Nitrogen is the primary nutrient of concern in the marine waters of the Peconic Estuary System. When nutrients are added to the estuary at excessive rates from sources including runoff, groundwater inflow, atmospheric deposition, and sewage treatment plants, the excess nutrients stimulate aquatic plant growth, including production of algae (including microscopic and larger plants that live in surface waters). Excess algae can lead to decreased dissolved oxygen in estuary waters, leading to less than favorable conditions for fish and other marine life. The increased production of algae caused by nutrient enrichment results not only in low dissolved oxygen conditions, but also discolors the water, decreases water clarity and diminishes the amount of light received by beneficial rooted aquatic plants, such as eelgrass. Because of the multitude of impacts excess nutrients can have on our local waters, it is the goal of the PEP to establish and implement rational preservation targets prior to degradation and occurrences of use impairments.