SCDES Provides Update on Lake Hartwell Harmful Algal Bloom before Memorial Day Weekend

FOR IMMEDIATE RELEASE:
May 22, 2025 

COLUMBIA, S.C. — The South Carolina Department of Environmental Services (SCDES) continues to monitor the harmful algal bloom (HAB) on Lake Hartwell in order to provide the latest recommendations for protecting public health.  

On May 19, SCDES’s Aquatic Science Division (ASD) teams surveyed the lake and collected new water samples from 17 different locations, as identified in the map graphic. SCDES’s Algal Bloom Monitoring Map has been updated with sampling locations and observations since May 19. According to ASD field teams, the algal bloom is still present in many coves and along the shore, but conditions may be improving compared to the previous full lake survey on May 6. 

The May 19 water samples indicate the continued presence of cyanobacteria (blue-green algae) capable of producing toxins. As with previous round of sampling, the concentration of the cyanotoxin cylindrospermopsin was below the analytical detection limit in all 17 samples. Microcystins were detected in all 17 samples. The maximum microcystins concentration observed in this sample set was 0.125 micrograms per liter, which is below the recreational standard of 8 micrograms per liter. 

Based on the latest round of lake observations and water sampling, the Recreational Watch for Lake Hartwell remains in effect, with the following recommendations: 

• avoid direct contact with lake water in areas where the HAB is observed
• keep pets and animals from swimming in or drinking from the lake in areas where the HAB is observed 

SCDES first issued a Recreational Watch for Lake Hartwell on April 30 after identifying the presence of a HAB. Cyanobacteria capable of producing cyanotoxins were observed in initial water samples and subsequent samples collected on May 6, but cyanotoxin concentrations were low or below the analytical detection limit as they are in the most recent samples. 

The most common symptoms associated with HABs are stomach pain, skin rash, headache, coughing and watery eyes. 

If a pet displays symptoms after coming into contact with a HAB, please consult with your veterinarian. 

SCDES will continue to monitor the Lake Hartwell HAB and communicate with local officials, stakeholders and the public. The agency is also in regular communication with the U.S. Army Corps of Engineers.  

As a reminder, HABs are a common occurrence in South Carolina lakes. They are typically observed during the warmer and drier months, and they can persist for several weeks. The blooms can look like bright green spilled paint or blue-green discoloration of the water. With cooler temperatures, heavy winds and rain, blooms may begin to break up and die off.  

For more information, contact SCDES’s Bureau of Water at 803-898-8374 or by email at HAB@des.sc.gov. If calling after hours, please leave a message that can be returned. For additional information about harmful algae in South Carolina, visit the SCDES HABs webpage and Algal Bloom Monitoring Map. 

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