Water Quality Issues
Who monitors water quality across the Edisto Island Watershed?
The South Carolina Department of Health and Environmental Control (SCDHEC) monitors surface waters across the state to characterize water quality, determine if water quality standards are being met, and identify areas that need attention. Ultimately, SCDHEC strives to maintain both state and federal water quality standards as directed by the Clean Water Act and the SC Pollution Control Act. Water bodies that do not meet set water quality standards are designated as impaired and placed on the 303(d) list. A Total Maximum Daily Load (TMDL) is developed for impaired sites within two to thirteen years to limit pollutant discharges.
What are the main pollutants of concern?
The primary pollutant of concern across the watershed is bacteria, indicated by measurements of fecal-associated bacteria, specifically enterococcus and fecal coliform bacteria. Elevated levels of these fecal bacteria serve as a proxy for other associated pathogens in the water that can pose a human health risk, particularly when consuming shellfish (such as oysters) harvested from high-risk areas. Elevated levels of bacteria can also make it unsafe to swim and other recreational uses of the water, particularly following heavy rains.
The secondary pollutant of concern across the watershed is sediment, derived from upland or stream bank erosion. Sediment in the water increases turbidity (cloudiness) and reduces water clarity. Sediment in waterways is often associated with additional pollutants such as chemicals and heavy metals which can attach to soil particles. When sediment clouds the water, less light can penetrate below the water's surface, which can affect plants and animals that live in the water. Edisto’s tourism-based economy is dependent on clean water. Activities like swimming, kayaking, charter fishing, and eating local seafood are primary draws for visitors, and these activities support the livelihood of many area residents. All of these can be affected by water pollution, and excess sediment deposition in waterways used for navigation can require costly dredging to solve.
How does water pollution affect shellfish harvests?
Shellfish, including oysters, clams, and mussels, are abundant in the waterways around Edisto Island. SCDHEC’s Shellfish Monitoring Program routinely monitors shellfish areas across the coast to ensure that both shellfish and the areas they are harvested from meet health and environmental quality standards. Monitoring results determine whether shellfish beds are rated as approved, conditional, or restricted for harvest. Select sites across the Edisto Island watershed have been monitored monthly, since the 1990s, for a variety of parameters, including bacteria. High levels of bacteria in the water pose a human health threat for those who consume shellfish, so ongoing monitoring establishes areas that are considered safe to harvest oysters for consumption and those that are not. Some of the shellfish areas around the Edisto Island watershed are currently classified as either restricted or prohibited.