The quality of Long Island’s coastal waters has been a topic of concern and discussion in recent years, with evidence of increasingly high levels of nutrient pollution and algal blooms emerging. Still, due to the disparate nature of water quality monitoring across Long Island, a comprehensive assessment of the quality of all of Long Island’s surface waters has been lacking.
The Long Island Index asked the Stony Brook University’s School of Marine and Atmospheric Sciences to compile data from multiple sources to provide a first ever view of Long Island-wide water quality. This analysis specifically combined data collected using uniform methods from The Gobler Laboratory at the University, Suffolk County’s Department of Health Services, and Town of Hempstead and examined two water quality parameters:
The results of this analysis is made accessible via the water monitoring overlays you can add to the Long Island Index map.
Water clarity is determined by measuring the depth in feet at which a white disc, known as a secchi disc, ceases to be visible from the surface. A high "secchi depth" means that water is relatively clear; low secchi depths indicate that the water is relatively murky.
Algae are measured via their primary pigment, chlorophyll A. Chlorophyll A levels are measured in micrograms per liter. High algae levels indicate that the water is relatively murky; low levels indicate that is relatively clear.
Water clarity is important from an ecological point of view, as seagrass, a critical fish habitat, needs high light levels to survive. Economically, home values have been linked to water clarity in many regions across the US, including Long Island.
A Long Island-wide view of water clarity shows large variability across Long Island. Water clarity is highest in regions on the East End (i.e. Peconic Estuary), eastern Shinnecock Bay, and the south shore bays of Nassau County. In south shore regions of Suffolk County, water clarity is low across Great South Bay, Moriches Bay, and western Shinnecock Bay. On the north shore, regions further inland such as back-harbor regions have lower water clarity whereas water in Long Island Sound has higher water clarity.
These trends are largely driven by differences in the levels of algae which, in general, show trends that are the opposite of water clarity. These trends are controlled by the extend of nitrogen pollution and water circulation: Very near shore regions with stagnant water and heavy nitrogen pollution have high algae levels and thus are murky. Conversely, regions with good water circulation such as zones near ocean inlets or zones further from land have low algae levels and thus better water clarity.