Water surrounding Sanibel and Captiva classified as impaired due to nutrient enrichment

The Florida Department of Environmental Protection’s (DEP) 2020-2022 Biennial Assessment Draft classifies the waters in Pine Island Sound, San Carlos Bay, and the J.N. “Ding” Darling National Wildlife Refuge as “verified impaired” because they exceed nitrogen and chlorophyll a standards designed to support a healthy ecosystem.

The DEP evaluates water quality data collected for waterbodies within 29 watershed basins throughout the state. If there is enough data to meet the state’s requirements, DEP will determine if the waterbody meets water quality criteria consistent with the federal Clean Water Act. The criteria are meant to protect the health of fish and wildlife and ensure that waterbodies are swimmable and fishable and, in some cases, meet standards for shellfish harvesting and drinking water.

In 2020, the DEP analyzed data, including new data provided by SCCF (Sanibel-Captiva Conservation Foundation), which indicate that the waters immediately surrounding both Sanibel and Captiva islands do not meet water quality standards. When waterbodies are identified as impaired, the DEP will develop a plan for reducing the pollutant of concern. In this case, the plan would focus on reducing the amount of nitrogen entering the waterbodies from the adjacent land uses.

In addition to the nutrients nitrogen and phosphorus, DEP considers concentrations of chlorophyll a in the water. Chlorophyll a is an indicator of how much algae growth is occurring. High levels of chlorophyll a indicate waters are enriched with nitrogen and phosphorus (eutrophic) and the ecosystem can become over productive, leading to oxygen depletion, fish kills, harmful algae blooms (HABs), and other ecological problems.