Recreation in the natural waters of the Chesapeake Bay region should always be approached with caution after rainfall. And, since mid-June, much of the Bay watershed has been walloped with rain.
Afternoon and evening thunderstorms plaguing the area have sent high volumes of stormwater rushing into streams, rivers and the Bay itself — carrying pollution with it. The influx triggered alerts about unsafe swimming conditions across the region.
In Maryland, frequent rainstorms prompted Anne Arundel County to issue 19 swim advisories through mid-July. That’s roughly twice as many as it issued for all of 2024, according to Jennifer Kenney, the department’s water pollution specialist.
“Oh, my gosh, so much rain,” she said.
According to the National Weather Service, most counties in Maryland and counties in northern and central Virginia saw 50% to over 75% more inches of rain than average over the last month.
Lancaster, York and Lebanon counties in Pennsylvania saw 75% more inches of rain than average, too.
Stormwater carries pollution that can harm both aquatic life and human health. In terms of recreational contact, the biggest concern is bacteria: The heavier the rain, the more likely the runoff contains sewage and animal waste.
State and county health departments, as well as nonprofit environmental groups and others, tackle the problem with a variety of water quality monitoring programs and efforts to inform the public. Those programs were in high gear as bacteria levels spiked in recent weeks and then, in many cases, returned to a safer range.
Water quality tests in freshwater environments usually look for the presence of Escherichia coli, or E. coli, which indicates the presence of raw sewage or animal waste. Most strains are harmless, but some cause illness in both people and pets, ranging from diarrhea to urinary infections and respiratory illness.
In brackish or saltwater environments, tests generally look for Enterococcus faecalis, commonly referred to as enterococcus. It, too, indicates the presence of sewage or animal waste and can cause significant illness.
Brackish water can also contain bacteria called Vibrio, which occurs naturally in the water. Spikes of Vibrio in warm water can cause an infection in open wounds that, while uncommon, can be fatal.
The risk of illness from any of these pathogens is greater for people with underlying health conditions.
Credit: Dave Harp
Credit: Dave Harp
Credit: Dave Harp
Credit: Dave Harp
Credit: Dave Harp
But if you want to head for the water, gauging the conditions for a particular day or location is often a challenge. The timing of water quality tests varies by site. Samples might be collected once or twice a week, biweekly or monthly. That means the latest results might not reflect conditions on the day you have in mind.
Officials typically say that you should check with your local river organization or health department for test results — but stay out of the water if there has been heavy rain in the last 48 to 72 hours. They also warn against swimming in water that appears muddy or clouded with sediment. Definitely don’t drink it.
Moreover, they recommend avoiding natural waters altogether if you have an unhealed cut or abrasion anywhere on the body. Water contact could lead to serious infections.
The Maryland Department of the Environment cautions that “swimming in natural waters is never risk free.” And even if there’s no reason to think the water is unsafe, it says, people should shower after swimming and wash their hands before eating.
MDE maintains a Healthy Beaches website, with an interactive map displaying the latest reported conditions at 188 public or community beaches monitored statewide.
But Tammy Domanski, director of the Environmental Center at Anne Arundel Community College in Maryland, cautions people against over-reliance on beach swim apps or websites that tend to simplify water conditions with red and green labels. Even if the most recent bacteria count at a particular place doesn’t go over the safety threshold, she said, people need to consider their own health status in deciding whether water contact is prudent.
Elle Bassett, riverkeeper for the Arundel Rivers Federation in Maryland, said it’s vital for people to find out whether it has rained at a given site in the previous 48 hours. She suggests consulting the National Weather Service website to check for precipitation that might have fallen in the area, particularly overnight when people may have slept through it. The website allows you to enter the Zip code of a swim site, then click on a link to show its three-day history of rainfall.
Widespread alerts
Storms hit hard in the lower Susquehanna River basin of Pennsylvania. Most of the 22 sites sampled weekly by the Lower Susquehanna Riverkeeper Association showed high levels of E. coli in each of the first three rounds of sampling in July.
Lower Susquehanna Riverkeeper Ted Evgeniadis said that both rural and more developed areas have been affected. In rural areas, stormwater can pick up bacteria from farms, including manure used as fertilizer on field farms or cattle defecating in creeks. In urban and suburban areas, bacteria more likely come from failing septic tanks, sewage system overflows and pet waste.
The Potomac Riverkeeper Network detected elevated bacteria in mid-July at 11 of the 30 sites it routinely monitors on both sides of the river from the District of Columbia downstream, including at National Harbor in Prince George’s County and Port Tobacco in St. Mary’s County.
Farther upriver, as of July 16, Upper Potomac Riverkeeper Brent Walls found that six of 14 sites had elevated bacteria. By July 23, only one site still had E.coli levels above the safe-swimming threshold.
Dean Naujoks, the Potomac Riverkeeper, said the group has detected more instances of high bacteria this summer, a development he attributes to the intensity as well as frequency of rain.
“This is climate change,” he said. “This is kind of the new norm, these insane flooding events.” Four inches of rain is a lot for a single rain event that’s not linked to a hurricane or nor’easter, he added, but “we’re seeing it more frequently.”
The Shenandoah River, the Potomac’s main tributary, was impacted too. The Friends of the Shenandoah River monitors bacteria levels throughout the valley, posting weekly results on its website.
On July 2, following heavy rain, none of the 12 sites the group monitors were considered safe. But two weeks later, on July 16, 10 had bacteria levels low enough to be considered safe for swimming. As of July 23, only one site on the Shenandoah — the Castleman’s Ferry boat launch in Clarke County, VA — had an E. coli count making it unsafe.
In general, the group has adopted the saying, “If it’s brown turn around.” If enough sediment has washed into the water to turn it brown, they say, it’s likely that unsafe bacteria levels are there as well.
Bacteria also impacted sites along the Bay’s southernmost major river, the James, where volunteers collect water quality data for the James River Association. The group shares its findings with the public in an online map. Nine of the 21 testing sites from Richmond to Hampton Roads exceeded the safety threshold for bacteria between July 11 and July 18. All were deemed in a safe range by July 24.
In the area of Virginia Beach, six of the 11 sites tested for enterococci in June — all in salty or brackish locations — exceeded the safe-swimming threshold. The highest reading was at Thalia Creek, which was more than 20 times above the limit.
In freshwater testing, five of the eight sites had E. coli readings above the limit, with the biggest spike at London Bridge Creek.
“If there’s more rain, that’s more stormwater,” said Cristin Pullman, community outreach manager for the nonprofit Lynnhaven River Now, which has been conducting monitoring for a decade. “If we don’t have proper ways of treating stormwater on both municipal and private land, the pollutants run right off into our creeks.”
Statewide, though, swimming advisories this year appear to be occurring at or even slightly below the pace of 2024, when the Virginia Department of Health issued 65 advisories for a total of 130 days. Through July 17 of this year, nearly halfway through the season, there have been 25 advisories.
On Maryland’s Eastern Shore, nearly half of the 54 sites failed tests for enterococci on June 17, according to monitoring conducted by the nonprofit group ShoreRivers. The highest recorded exceedance was at Trappe Landing in Talbot County. Conditions improved in July, but only slightly, with 21 sites still showing levels above the safety threshold in July 24 testing.
In May alone, that area saw 9.5 inches of rain, about five inches above the 10-year average. June received another 4.5 inches, about 2 inches more than usual.
The timing of those storms may have boosted recorded bacteria levels, said Miles-Wye Riverkeeper Ben Ford — much of the rain falling between Tuesdays and Thursday mornings. Because the group’s volunteers canvass the region on Thursdays, they’re probably capturing the bacteria population at or near its peak each week, Ford said.
Baltimore does not have any public beaches and does not routinely monitor water quality for swimming safety. In fact, city officials normally recommend not swimming in the harbor or anywhere in the Patapsco River or its tributaries.
The task of water quality monitoring in the city has been picked up by two nonprofits — the watchdog group Blue Water Baltimore and the Waterfront Partnership, a coalition of businesses, tourism attractions and local officials.
Blue Water Baltimore routinely checks water quality at 51 spots in the Patapsco River watershed. Of the 12 sites it monitors nearest the Inner Harbor, the group’s website shows that five had elevated bacteria in samples taken the first or second week of July. Sites tested in the Jones and Gwynns Falls also showed elevated bacteria levels, as did those in Herring Run.
Organizers of what would have been Baltimore’s second annual Harbor Splash rescheduled the June event due to rain and then canceled the July date after showers the night before pushed the bacteria count above the acceptable threshold. They said the “unusually rainy spring” had made conditions “less than ideal.”
South of Baltimore, Anne Arundel County is a hotspot for water recreation of all types. From Memorial Day through Labor Day, the county health agency tests for bacteria weekly at 17 public beaches and campsites and biweekly at more than 60 other less heavily used community beaches. River groups and the Anne Arundel Community College conduct independent sampling, too.
“We’ve tested for 8 weeks and six of those eight have had over a half inch of rain,” said Bassett of the Arundel Rivers Federation, which monitors the South, West and Rhode rivers.
As a result, only about 45% of the water samples the group collected through mid-July yielded bacteria levels considered safe for swimming. Last year, she noted in a blog post, the pass rate was more than 80%.
Bassett said the high failure rates have upset some residents, who have questioned the group’s testing methods. But she said the only thing different this year is the weather.
Even open water areas, which are usually safer, can have bad days. Anne Arundel issued a health advisory July 9 for Mayo Beach Park, a popular spot for swimming, wading and kayaking at the mouth of the South River. It was lifted a week later. Until then, the park had never been under a swim advisory or closure since monitoring began in 2000, according to the MDE.
Awareness and funding
Potomac Riverkeeper Dean Naujoks and other water quality watchdogs say they’d like to see better public notification of water monitoring results because “a lot of people aren’t going to go to a website” to see the latest results before wading into the water.
“[At] a lot of agencies, whether it’s Virginia, Maryland, or the District of Columbia, it’s not easy to find the information,” he maintained, “and there’s not consistent reliable data.”
And even when data is available, results can be surprisingly variable, even from one side of a river or stream to the other. Testing on July 16, for example, indicated that the western shore of the Potomac River at Belle Haven Marina in Alexandria had safe bacteria levels while the National Harbor, right across the river, did not. The National Harbor location is now regularly open for public swimming events, but only when the water quality testing shows it is safe to do so.
Evgeniadis, the Lower Susquehanna Riverkeeper, said that funding for water quality programs has declined over the last 20 years and that he has seen participation by community scientists and watershed groups drop off. His organization is the main group tracking bacteria in the lower river basin.
“It’s very, very crucial that our federal government funds water quality monitoring programs, our [U.S. Geological Survey], our universities, those that are actually on the ground doing this work,” Evgeniadis said. “You can’t do this work without money.”
Staff writers Jeremy Cox, Lauren Hines-Acosta, Whitney Pipkin and Timothy B. Wheeler contributed to this article.