HORRY COUNTY, S.C. (WBTW) — The South Carolina Department of Health and Environmental Control (DHEC) will soon start monitoring water at South Carolina beaches for bacteria levels.

The program runs yearly May 1 through Oct. 1 when the waters are warm enough to swim.

DHEC currently monitors 122 locations. The 10 in North Myrtle Beach and 12 in Myrtle Beach will be tested weekly.

DHEC looks for high levels of enterococcus bacteria. The bacteria can cause gastrointestinal issues.

Bryan Rabon, manager of aquatic science programs with DHEC, said bacteria levels are highest after bad weather.

“The biggest thing that I think I want folks to be aware of when they come to the beach is after a rain event is when we generally see the elevated bacteria. Any other time its a good time to be in the water,” Rabon said.

Rabon said the bacteria usually comes from sewer overflow and pet waste that gets washed into the ocean.

DHEC will issue a swim advisory if levels of bacteria get too high. It issues a short term, or temporary advisory, if consecutive samples return higher levels of bacteria than are allowed.

Follow-up sampling is performed daily, and the temporary advisory is removed when the bacteria levels drop back to acceptable levels.

Long-term swimming advisories are put in place for locations with an increased possibility of high bacteria levels — especially following rain events — due to stormwater runoff. The long-term advisories and signs are typically located where stormwater from pipes or swashes — small creeks — flows across the beach to the ocean.

A long-term advisory is issued for areas where more than 10% of the enterococcus data collected over the past five years exceeds the acceptable levels for recreational use. Temporary advisories are not posted where long-term advisories already exist.

A swim advisory does not mean the beach is closed. Wading, fishing and collecting shells will not pose a risk.

Rabon said one area of the beach commonly affected is swashes.

“For children playing in swashes we really do not recommend that,” Rabon said. “That is not the ocean water. That is actually water that has run off of the land. It’s come off of parking lots, it’s come off of parks and everything. So, it’s not the ocean water that you’re expecting it to be and there’s elevated risk for anyone being and swimming in that water.”

He said to always check bacteria levels before planning a trip to the beach. The DHEC website or their Check My Beach program will list any advisories.