How dangerous are bacteria in SC ocean waters and when do they cause beach closures?
Have you ever made your way down to the beach, but noticed a sign telling you that it wasn’t safe to swim?
The South Carolina Department of Environmental Services conducts water sampling and testing across 122 beaches in the state, stretching from Cherry Grove Beach to the south end of Hilton Head Island.
These tests are conducted twice a month from May to October across the state, but Myrtle Beach area beaches are sampled weekly, according to the SCDES.
What do they test the water for?
The SCDES largely tests for enterococci bacteria. It’s commonly found in the human gut and urinary tract and can cause skin, eye, ear and respiratory tract infections.
Other kinds of bacteria tested for that can be found in ocean waters include:
E. coli: A common bacterium that can cause diarrhea, stomach cramps and vomiting.
Vibrio: A bacterium found in coastal waters, especially during warmer months, that can cause diarrhea, nausea, fever and wound infections.
How does it get into the water?
These bacteria, primarily originating from human and animal waste, can enter the ocean through various pathways, including leaking septic systems, stormwater runoff, sewage overflows and animal waste.
All of the various pathways lead the bacteria to the water and can cause closures.
When do they close areas of the beach?
If the bacteria levels exceed established safety thresholds, the beach is deemed unsafe for swimming.
That threshold is 104 MPN/100mL, which refers to the most probable number of bacterial colonies per 100 milliliters of water.
Once that threshold is met or passed, a long-term advisory is put in place to minimize the risk of illness for beachgoers.
Common culprits leading to beach closures and advisories include excessive rainwater that carries pollution from storm drains, sewage and chemical spills, or after heavy rains, according to the National Oceanic and Atmospheric Administration.
What are the different types of advisories?
Advisories mean that you should not swim in those areas of the water. The SCDES states that young children, the elderly and those with compromised immune systems are particularly at risk in these waters.
The SCDES issues two different kinds of advisories for beachgoers.
Temporary/Short-Term Advisories: These are issued during the swimming season (May 1 to Oct. 1) when water samples show elevated bacteria levels. They are often triggered by heavy rainfall, which can wash pollutants like bacteria into the ocean. These advisories typically only last one to two days.
Long-Term Advisories: These are issued for specific locations where there’s a persistent concern about bacteria levels, often linked to stormwater runoff or other sources that consistently contribute to contamination. These areas are reevaluated annually and closed for longer periods of time.
Advisories do not mean that the beach is closed. Activities like wading, fishing and shell collecting do not pose a risk.
To see if there are any active advisories, the SCDES lists them here. You can also visit the SCDES Beach Guide to see when beaches were last inspected.
This story was originally published July 18, 2025 at 6:00 AM.
