Water Quality on Cumberland Island

By Dani Purvis & Sierra Abbasi.

Anyone who has had the pleasure of visiting Cumberland Island can attest that its remote, largely undeveloped state supports a striking amount of biodiversity teeming with wildlife. Clean and uncontaminated freshwater, brackish, and saltwater sources across and around the island are critical to the abundant life that draws tens of thousands of visitors to this magical island annually. The saltwater marshes usher you from the St. Marys ferry to the docks on the western side of the island; the 2500 acres of freshwater ponds and wetlands are dotted within the maritime forest; the protective saltwater coves on the shoreline line the eastern side of the island; and the entire island is nestled within an estuary where the ocean meets the confluence of the Satilla, East, and St. Marys river inlets. The value of clean water cannot be underestimated in one of the few undeveloped shorelines on our Southeastern coastline.

We, as investors in our public lands, have a right – and a collective responsibility – to be informed about the state and conditions of Cumberland Island National Seashore and other national and state parks. It is in that vein that a small team of two volunteers from Wild Cumberland dug into the latest publicly available water quality datasets from 2017-2022 to evaluate the overall status of water quality on and around the island and translate these results into a more understandable format for the general public. If you’ve ever read a water quality report, you will understand me when I say: you’re welcome. 

Water Quality Monitoring On Cumberland Island

We looked at water quality reports from 2017 to the most recent report and identified three primary reports with comprehensive water quality testing conducted by the Southeast Coast Network (SECN). To maintain and protect Cumberland’s waters, the SECN conducted a two-pronged approach to monitoring Cumberland’s estuary waters, including long-term monitoring from January 2017 to December 2019¹ and two short-term monitoring periods during  2017² and 2022³. Short-term sampling periods took place during August 2017 and July 2022. The long-term data was collected from January 2017 to December 2019, with a gap from July 2018 to February 2019. Maps of testing sites are provided in the appendix below. 

Along the estuarine western bank of the island, the SECN teams collected water samples in 30 randomly selected sites, which varied during each sampling period. They measured the big 5 water quality indicators (i.e., dissolved oxygen, pH, salinity, temperature, and turbidity) and nutrient levels (nitrogen, phosphorus, and chlorophyll a), and sediment quality at different times of day and year to find seasonal and daily patterns. We provide a glossary of water quality indicators below so you don’t have to Google any terms!

Cumberland Island Water Quality Results 2017-2022

The water quality results were generally positive with no major red flags. During the long-term sampling period from 2017-2019, mean dissolved oxygen levels ranged from good to fair, which remained true for the short-term data collection as well. During both long-term and short-term sampling periods, the pH, salinity, and temperature all fell within a satisfactory range. Unsurprisingly, water clarity (i.e., turbidity) ranged from poor to good at the Sea Camp dock, which has the highest volume of boat traffic on the back bay, but all other sites reported good water clarity during both short-term monitoring periods. 

Dissolved inorganic nitrogen was a concern in 2017, but improved to a status of “good” at all 30 sites in 2022. Dissolved inorganic phosphorus and chlorophyll a levels also showed similar improvements from 2017 to 2022. During 2017, sediment quality was also tested for a set of contaminants, and 97% of sites were rated good; only one site was rated fair. 

Overall, Cumberland Island’s saltwater and brackish water quality seemed to be improving and healthy over a 5-year period. However, freshwater quality data are missing from our comprehensive understanding of the island’s water quality. The freshwater ponds and lakes on the eastern side of the island should be tested; much of the island’s fauna and migrating shorebirds rely on these freshwater sources for survival. Based on the data available, there has been a slight improvement in the island’s water quality in the last decade, and we hope that future data will maintain the trend. 

Potential Threats To Water Quality On Cumberland Island

Reassessing water quality indicators at regular intervals is essential to tracking the impacts of potential threats to Cumberland Island’s welfare. Although barrier islands are subject to constant transformations, the human impacts from all sides are reshaping the island more rapidly than natural forces. 

Saltwater intrusion (or contamination) of the low-lying freshwater wetlands due to sea level rise and flooding from tropical storms and king tides has been previously documented^4-5, although there is a notable lack of studies on the impacts of saltwater intrusion within the last 20 years. Prior research has found low dissolved oxygen concentrations to be the most significant water quality problem on Cumberland Island. In other words, high temperatures and high salinity from saltwater intrusion can choke out the oxygen that freshwater species need to survive. Loss of freshwater sources also threatens the welfare of the terrestrial residents of the island, including the hundreds of migratory bird species that stop on Cumberland Island on their way along the North Atlantic flyway.   

Along the back bay, increasing storms and flooding increase the threat of runoff and contamination of PFAS or “forever chemicals” from the King’s Bay naval base, which lies only a few miles west of Cumberland^{5, 7}. PFAS are chemical compounds that break down slowly and can cause health problems like cancer, liver and thyroid problems, and other serious health issues.  In 2021, EWG identified five types of PFAS in the Kings Bay groundwater, which they suspect are from firefighting foam. On Climate Central’s Surging Seas Risk Finder, you can toggle the speed of sea level rise to determine the future likelihood that Kings Bay will experience flooding above 4’.  

Increasing tourism from a proposed ferry route from Fernandina, Florida, to St. Marys could also bring an increase in pollution and contamination in the coastal waters along the southern tip of the island⁸.

.On the national stage, the US House of Representatives voted in late June to advance a bill that would reduce the regulatory authority of the Clean Water Act⁹. Critics of the bill, including us folks at Wild Cumberland, argue that the bill will make unpermitted industrial pollution of watersheds easier, make it harder to seek legal justice against environmentally harmful projects, and weaken federal agencies’ ability to enact water protections.

So What Does It All Mean, And What Can I Do?

Within a 5-year period, the SECN reported acceptable or good water quality for Cumberland Island across nearly all indicators. As long as the NPS, USGS, NOAA, and federal agency partners report water quality testing results, Wild Cumberland will continue to evaluate these results to ensure the island is being responsibly stewarded. We will also keep an eye out for the numerous threats to the island’s waters to ensure the public remains informed.      

If you are interested in getting involved in water quality monitoring, there are a lot of opportunities for citizen scientists to volunteer with local organizations, such as the St. Marys Riverkeeper, to collect and evaluate water quality projects. 

If you see something concerning, such as illegal dumping or potential contamination in a water source on or around Cumberland, report your concern to Wild Cumberland here and take geotagged photos if possible!

Finally, if you appreciate the vital role that the Clean Water Act plays in keeping you and your community safe by protecting our waters, contact your representatives now and tell them to vote No on the Water Quality Criteria Development and Transparency Act (H.R. 3888), the Water Quality Standards Attainability Act (H.R. 3934), and the Confidence in Clean Water Permits Act (H.R. 3897) because you are concerned about the threats to water quality and public health. Find your representatives here!

Appendix

Water Quality Testing Site Maps

Glossary of Water Quality Terms

• Dissolved oxygen: The amount of oxygen found in water. Low dissolved oxygen levels can choke out marine life. 
  
• pH level: A measurement of how acidic or basic a substance is. Low pH represents a higher acidity, causing a hostile environment for marine life.
  
• Salinity: How much salt is dissolved in water. Higher salinity decreases dissolved oxygen and increases pH levels.
  
• Temperature: How warm or cold the water is. Warmer waters have lower dissolved oxygen levels.
  
• Turbidity: How clear a fluid is; this can affect the amount of sunlight that can reach aquatic plants and visibility for marine animals.
  
• Nitrogen: Measures the nitrate levels in water, which can cause eutrophication (i.e., high nutrient levels) and low dissolved oxygen levels. Nitrates typically come from sewage runoff and fertilizers. 
  
• Phosphorus: Measures the phosphate levels in water; high levels can cause eutrophication and low dissolved oxygen levels. Its sources are typically sewage and urban runoff, as well as fertilizers.
  
• Chlorophyll a: It is a key indicator of the amount of algae and plant biomass in the water, which absorbs light energy, a photosynthetic process that converts carbon dioxide and water into oxygen and carbohydrates that aquatic life needs.
  
• Sediment quality: Measures the materials settled at the bottom of the water, an indicator of metal and other chemical concentrations in a body of water. High levels of toxic substances can be damaging to the health of marine life. The SECN tested for total organic carbon, sediment grain size, metals, mercury, as well as other pesticides, and compounds (PAH, PCB).

Sources

1. Starkey, E.N., & McCay, D. (2021). Fixed-Station Water-Quality Monitoring at Cumberland Island National Seashore 2017–2019 Data Summary. Available at: https://irma.nps.gov/DataStore/DownloadFile/666318
2. Starkey, E.N., Wright, W., & Cooper, C. (2024). Assessment of Estuarine Water and Sediment Quality at Cumberland Island National Seashore: 2017 data summary—version 1.1. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2304403 
3. Starkey, E.N. (2024). Assessment of Estuarine Water Quality at Cumberland Island National Seashore: 2022 Data Summary. National Park Service, Fort Collins, Colorado. Available at: https://www.nps.gov/articles/000/secn-parkwide-assessment-cuis-2022.htm
4.  Frick, E. A. (2002). Water quality and aquatic communities of upland wetlands, Cumberland Island National Seashore, Georgia, April 1999 to July 2000 (Vol. 2, No. 4082). US Department of the Interior, US Geological Survey.
5.  Union of Concerned Scientists. (2016). On the Front Lines of Rising Seas: Naval Submarine Base Kings Bay, Georgia. https://www.ucs.org/resources/front-lines-rising-seas-naval-submarine-base-kings-bay-georgia#:~:text=During%20the%20second%20half%20of,severity%20of%20storm%2Ddriven%20flooding
6.  Alber, M., Flory, J., & Payne, K. (2005). Assessment of coastal water resources and watershed conditions at Cumberland Island National Seashore. Technical Report NPS/NRTC-2005/332, National Park Service, Water Resources Division.
7.  EWG. (n.d.) 720 Military Sites With Known or Suspected Discharges of PFAS. Webpage available at:  https://www.ewg.org/interactive-maps/2020-military-pfas-sites/map/ 
8.  Wilcox, Z. (2025, April 16). St. Marys plans ferry to connect with Fernandina Beach. First Coast News. https://www.firstcoastnews.com/article/news/local/st-marys-plans-ferry-fernandina-beach/77-ed6fe56e-096c-4ef2-9739-96b0e6b0b73a 
9.  NRDC. (2025). House Committee Advances Bill That Guts Clean Water Act. https://www.nrdc.org/reaction/house-committee-advances-bill-guts-clean-water-act