Swimmers warned in opposition to taking a dip after heavy rains

Earlier this week, nine of 11 spots on Columbia’s major rivers showed bacteria levels high enough to prompt temporary warnings against swimming.

But that wasn’t surprising to Congaree Riverkeeper Bill Stangler, whose organization tested the water and issued the advisories. The high bacteria levels, which followed downpours in the Columbia area, verified the threat people face when they swim in natural waterways after heavy rains, he said.

In effect, swimming after rainstorms is the worst time to take a dip in a river, lake or the ocean, particularly in urban areas where stormwater pipes direct pollutants off the land, he and others said.

Soaking rainfall often sends stormwater rushing into rivers like the Congaree, Broad and Saluda, raising bacteria counts and indicating the presence of germs that can make swimmers sick, Stangler said. Particularly heavy rains also can cause sewer spills.

The threat isn’t unique to the Columbia area. Communities across the state, including South Carolina’s popular beaches and tidal rivers, also are at risk for swimmers after heavy rains because of soaring bacteria.

“If you know that it just rained or there is a swimming advisory, be thoughtful and avoid those areas, or say ‘I’m not going to dunk my head under,’’ Stangler said, noting that swimming in muddy water can indicate a problem.

The Congaree Riverkeeper organization, which monitors water quality in the lower Saluda, Broad and Congaree, has been testing the rivers for years in the summer and posting its results to a website called howsmyscriver. The website keeps the latest information about water quality testing. The riverkeeper group issues advisories urging people to swim when bacteria exceed safe levels.

In the test results this past week, only two areas – on the upper part of the lower Saluda and the upper part of the Broad – had low enough bacteria levels for safe swimming. Those testing stations are in areas with fewer stormwater pipes that could compromise water quality.

In contrast, one of the most popular swimming spots on local rivers, the Saluda just above Riverbanks Zoo, was among areas tested that had bacteria counts higher than the safe standard, according to results from earlier in the week. Bacteria was more than twice the safe standard for swimming, according to the riverkeeper’s test results from June 18.

“Everything we are looking at indicates this was stormwater driven,’’ Stangler said. The high bacteria counts were less likely the result of sewer spills than runoff, because the elevated pollution counts “were so widespread, not at one specific site,’’ he said.

Stangler said a second round of test results that came in Friday, June 19 showed the bacteria had come down to safe levels at all the riverkeeper’s sampling sites.

Still, even those results must be taken in context. It can take 24 hours to get results back after sampling.. That means water conditions could change from the time the tests are taken and the results are available for release to the public. Updated test results from Columbia rivers, for instance, showed improved water quality Friday, but it has rained since the tests were taken, making it possible bacteria counts rose again

The problem can be notably worse when heavy rains fall after extended dry periods. Contaminants that have built up on the land are flushed into the water. That can include bacteria from pet waste or fertilizer, as well as chemicals.

To be safe, state officials say it’s prudent to wait 48 hours between rain storms before swimming in natural bodies of water.

At issue is the threat of illness for people exposed to bacteria in the water. Those who get water in their mouths can get upset stomachs or fever, while swimmers with open cuts can get infections from contact with the water. That’s mainly a threat to swimmers, but boaters also must be aware as they have water splash onto them..

Cheryl Carmack-Smith, a spokesperson for the Charleston Waterkeeper, said some areas where her organization samples, such as at Shem Creek, have high bacteria levels half the time, even when it has not rained. Septic tanks are believed to be the cause of the high bacteria, even in dry weather.

But when storms arise and rains fall, “those numbers spike and they are way worse,’’ Carmack-Smith said. “When we have dry periods and then we get heavy rain, it’s really bad.’’ She noted that when rains are scarce, that generally is “really good for our water quality.’’

Because of the threat, some communities are working to lessen the effect of polluted stormwater on rivers, lakes and the ocean.

In the Columbia area, for instance, Stangler said he has had discussions with local governments and planners about improving vegetated buffers along waterways. Vegetation, such as grass or shrubs, can filter out pollutants before they reach rivers. So can artificial wetlands.

For more than 30 years, leaders in the Myrtle Beach area have struggled with how to remove stormwater pipes from the seashore. The pipes were originally installed to get water off the streets following rains.

But as local leaders later found out, the drainage water contains bacteria that pools up on the beach and trickles into the ocean where people swim. Local governments along the Grand Strand have been working for decades to remove beach drainage pipes and replace them with long pipes that send the stormwater offshore beyond the breakers.

The S.C. Department of Health and Environmental Control, the predecessor agency to the Department of Environmental Services, has historically told people to be careful about swimming in the ocean following heavy rains. It also has urged caution against swimming in tidal creeks that flow into the ocean after rainstorms.

The department tests ocean water during the summer and early fall at 122 beach monitoring stations from North Myrtle Beach to the southern end of Hilton Head Island. Sampling is done every other week, except on the Grand Strand, where it is done weekly.

Signs the agency posts on certain stretches of beach say high bacteria levels may be in the water, “especially in days following rain due to stormwater runoff.’’

The agency reiterated that advice Friday.

“Don’t swim in the ocean or in rivers or lakes during or immediately following rainfall,’’ according to an email from the agency’s media relations department.

“To further reduce risk of illness, wait at least 48 hours after a heavy rain to resume swimming. In ocean water, heavy rain can wash bacteria and possibly harmful pathogens into the surf and high bacteria densities persist in the surf for hours after these rains, which may increase swimmers’ risk of illness.’’

This story was initially revealed June 20, 2026 at 6:00 AM.