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Children play in Myrtle Beach's 68th Avenue swash on Friday, June 1, 2018. Swashes and drainage pipes on the beach along the Grand Strand are more likely to contain harmful pathogens and are covered by long-term swimming advisories. Chloe Johnson/staff

MYRTLE BEACH — On a recent Friday on the north end of the beach, the sun was shining, tourists were tanning and children played in a swash. 

The murky stream, at 68th Avenue North, is one of several areas along South Carolina's most popular resort destination where water that runs off of roofs, roads and parking lots washes directly onto the beach.

Officials say wading and shell collecting there are generally safe, but it's still the most likely place to find elevated bacteria levels. As a result, this swash — a shallow channel of water cutting through the sand — along with 12 other runoff pipes and streams, carry a long-term caution not to swim within 200 feet of where they dump into the ocean.

But it's easy to miss signs near the dunes that warn: "SWIMMING IS NOT ADVISED."

The Grand Strand's landscape — a highly developed stretch of hotels, vacation homes and businesses along an elongated bay — means that when rain falls in and around Myrtle Beach, it doesn't have many opportunities to get absorbed back into the earth. Most makes its way to the ocean, and it's common for a quick, hard rain or tropical storm to trigger a water-quality advisory. 

One rain event just over a week ago sparked the S.C. Department of Health and Environmental Control to warn against swimming on all of Horry County's beaches. The May 29 blanket advisory was lifted a day later and replaced with localized warnings in North Myrtle Beach and Surfside Beach that lasted a brief time after. 

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Warning signs posted around swashes and drainage pipes in Myrtle Beach are sometimes not noticed by tourists. Storm water drainage that empties directly on the beaches along the Grand Strand is more likely to contain harmful pathogens and is covered by long-term swimming advisories. Chloe Johnson/staff

The two main cities in the area have been working for decades to correct the problem, primarily by routing water into deep-water outfall pipes that send runoff further out into the ocean, past the shore area where people swim.

"With everything we’ve built, from detention ponds to debris traps, and regional storm water systems to deep water outfalls, our ocean water quality is much better today than it was when we started addressing these issues, some 25 years ago," Myrtle Beach spokesman Mark Kruea said. 

But those fixes have been costly. North Myrtle Beach is also in the midst of an expensive and lengthy process of building the underwater pipes. In smaller towns like Surfside Beach, the costs are so prohibitive that deep-water outfalls aren't an option. 

"Those pipes are not even discussed because of the expense that comes along," Mayor Bob Childs said.

'Great strides'

The origins of the Grand Strand's storm water challenges stem in part from the original design of Ocean Boulevard.

The S.C. Department of Transportation's engineering, completed in the middle of last century, included runoff pipes that emptied directly onto the beach. Swashes, which remain from the original landscape of the area, also send water over the beach and directly into the ocean. 

Those features, combined with a high water table and a lot of impervious surface near the shore, make managing storm water both tricky and expensive. So far, Myrtle Beach has spent $37.5 million on four outfall pipes. North Myrtle Beach has installed five, at a cost of $26.7 million. Each outfall pipe combined runoff from multiple smaller pipes or swashes.

"We really have made great strides," Kruea wrote. "The subject is an easy target for the naysayers who aren’t concerned with the details, but just seek to criticize."

Still, the Grand Strand is the only region of South Carolina's coast that has permanent, long-term ocean swimming advisories.

In the Lowcountry, including around the Charleston area, swimming advisories due to poor water quality are rare. A sudden rush of storm water or a sewage leak is more likely to result in shellfish bed closures, such as the one spurred earlier this year after a sewer leak in the tiny Charleston County town of Hollywood. The beaches remained unaffected. 

DHEC lists all of its bacteria findings on a public website. But the specific bacteria it tests for, enterococcus, doesn't necessarily make swimmers ill.

Susan Libes runs the water monitoring lab at Coastal Carolina University and has tested along the Grand Strand since 1997. She said DHEC's tests mostly do a good job of indicating whether fecal matter is in the water.

Humans are most likely to get sick if they're exposed to the gut bacteria and viruses of other people. Enterococcus, however, is also present in the guts of other animals, including dogs, Libes said. 

"There’s a recognition that this is an imperfect tool," she said. "When you measure a high enterococcus level, you have the question in your mind: What risk does this really represent if there’s no human-sourced bacteria?"

Cleaning the water

Retention ponds can slow down storm water and filter it. As water sits in the ponds, particles settle at the bottom, and any pollutants attached to them stay there. 

Erik Smith, of the University of South Carolina's Baruch Institute of Coastal Ecology, said that in research he's conducted, correctly engineered ponds trap 90 to 98 percent of that type of bacteria. 

But the best method of making sure dirty water doesn't make it to the ocean, he said, is an all-of-the-above approach: In addition to ponds, absorbing water with vegetation, minimizing impervious surfaces and educating people to stop introducing pollutants all help. 

"It really does make a difference when you pick up your dog waste," Smith said. “It all adds up.”

In Myrtle Beach, every time the city works with an engineer on a new deep-water outfall, officials try to incorporate the most up-to-date methods of filtration to clean the water before it reaches the ocean, Public Works Director Janet Curry said. 

"Each outfall is different and unique to itself," she said.

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A couple sits in a Myrtle Beach swash as it empties into the ocean on Friday, June 1, 2018. Swashes and drainage pipes on the beach along the Grand Strand are more likely to contain harmful pathogens and are covered by long-term swimming advisories. Chloe Johnson/staff

Some screens separate the oil that builds up on roads from rainwater, while others separate out sediment. And other sections capture floating trash. By the time water reaches one of the outfall pipes, under the Myrtle Beach Boardwalk at 14th Avenue North, it's gone through three levels of filtration in underground pipes, Curry said.

As cities invest in building more of those systems, the Grand Strand still faces long-term swim advisories. The likelihood of getting sick, Libes said, depends not just on contact with runoff water but on a lot of factors, such as age, swimming with an open cut or having a compromised immune system. 

"A lot of people will tell you, 'Oh, I have swum in this water for 20 years, and I'm fine,'" Libes said. "And that’s part of this risk management, that they’ve taken in this information and made a decision personally for themselves.”

Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.