Two interns from the South River Foundation test the waters at Hillsmere Shores Community Beach. (Algerina Perna/Baltimore Sun video)

The start of summer lures many Marylanders to the Chesapeake Bay and area rivers for a dip along the shoreline. It also brings increased monitoring of beach and water quality, and sometimes dire warnings about bacteria levels.

This week, South Riverkeeper Diana Muller took 11 water samples along beaches south of Annapolis. All but one tested above safe swimming limits, prompting her to post the bacteria counts on Facebook with the caption: "I just received my bacteria results — PLEASE DO NOT SWIM in the SOUTH RIVER!!"

Stormwater, wildlife waste, sewage leaks and other factors add to bacteria in the rivers and bay, which can make them unsafe for swimmers who risk upset stomachs, diarrhea, eye and ear infections, and other illnesses.

Anne Arundel's coastline, with 533 miles of waterfront dotted with more than 100 community beaches, becomes one of the most tested regions in Maryland in summertime. Not only is routine water testing performed by the county Health Department but also environmental groups and private waterfront communities, creating what many consider the state's most robust effort to police beaches.

The county's Health Department issued no-swim advisories this week for three beaches in the county — Londontown on the South River, Beverly Beach on the Chesapeake and Upper Magothy Beach in Severna Park — after tests found high levels of enterococci, a bacterium found in the waste of warm-blooded animal. Earlier this month, officials warned people of potentially dangerous levels of bacteria in the water days before the annual Great Chesapeake Bay Swim.

The advisories, and the yellow warning signs posted on the beaches, stay in place until the bacteria counts come down, said Gerry Zitnik, a Health Department program manager who oversees testing at more than 90 beaches in Anne Arundel.

"There are some people that maybe ignore the warnings and go into the water," Zitnik said. "We try to give people the best information possible so they can make good decisions on their own whether they and their family members should swim in the water."

All Maryland counties with shorelines test water quality and use criteria from the federal government to designate "bathing beaches" where bacteria testing must be done.

In Anne Arundel, the most popular beaches — including Sandy Point State Park near the Bay Bridge — get weekly tests. Smaller and less popular beaches have biweekly or monthly tests.

While enterococci is just one of many water contaminants that can cause problems for swimmers, officials only test for that one. "It's an indicator organism that tells us other things may be there that may be potentially harmful," Zitnik said.

In Anne Arundel, the government's monitoring program is supplemented by a network of environmental and neighborhood groups that pay for testing at dozens of additional sites in cooperation with Anne Arundel Community College.

"As a big, large county with so many waterways that run through it … I think there's a much bigger attachment to the water," said Anne Arundel County Councilman Chris Trumbauer, who is riverkeeper and executive director for the West/Rhode Riverkeeper organization in southern Anne Arundel.

In each case, a trained worker or volunteer takes a sample of water. The samples are taken back to a lab, where the bacteria is grown on special media and counted under a microscope. It takes at least 24 hours to get results, which are reported as numbers of colonies per 100 milliliters of water.

For most beaches, the limit for safe swimming is 104 colonies. In some cases, though, beaches have counts well into the hundreds or thousands of colonies.

Riverkeepers such as Muller and Trumbauer and private communities don't have the authority to issue advisories at beaches — those can only come from the county government. But they can post the data on their websites and send email blasts warning people not to swim.

"My philosophy is transparency and letting people know that they're swimming in ooey-gooey yucky water," Muller said. Her organization, the South River Federation, also flies a bright red flag from the office that's visible from the river whenever bacteria counts are high.

"Because we're not a regulatory agency, we can't close the river down," she said. "But being a riverkeeper, I can caution people about it."

Trumbauer said his weekly bacteria count emails for the West and Rhode beaches are the most-read of all the messages his organization sends out. And the messages often get forwarded.

"All I can do is make people aware," Trumbauer said. This week's sampling on the West and Rhode rivers showed 13 of 14 sites with unsafe bacteria counts.

The Maryland Department of the Environment gets about $70,000 a year from the federal government for the water testing. Funding is expected to decline because of the budget cuts known as sequestration.

Most counties with shorelines post online updates on any beaches that have been closed or where bacteria levels have tested high.

Baltimore County tests water every other week at a dozen beaches, according to Health Department spokeswoman Monique Lyle. When bacteria levels are too high, the county closes the beach, posts signs and puts the information on the county website.

The state coordinates efforts in the various counties to ensure they use the same standards. The state helps with publicity, too, distributing signs and fliers to the counties.

But it can be a challenge to get people thinking about safety when they're at the beach, said Kathy Brohawn, an environmental program manager with the state Department of the Environment.

"There's always a group that is on the websites all the time, and some that, no matter what kind of outreach you do, you'll never get to them," she said. "We're always looking for new ways to get information out."

Behind the bacteria

Multiple culprits are behind high bacteria counts.

Stormwater is the top reason for bacterial contamination. When it rains, water rushes along pavement, picking up animal waste, trash and other contaminants that get flushed into creeks, rivers and the bay.

Other potential sources include animal waste — especially from geese and ducks — as well as sewage spills or leaks.

Stormwater runoff is the likely cause of high readings in Anne Arundel recently, Zitnik said.

"This time of year, particularly with these monsoon-like rains we've been having over the last two or three weeks, the high bacteria results could be a result of stormwater rushing into the waterways," he said.

Stormwater is such a concern that the county and state have a standing advisory warning people not to swim within 48 hours of a rainstorm. The county Health Department doesn't even take water samples after rainfalls because they know counts will be off the charts.

Private groups, however, test even after rains. "I want to give people the real data," Trumbauer said. "I know people go out the day after it rains and want to go swimming."

Trumbauer said people should be outraged that stormwater is such a problem that simple rain makes it unsafe to swim.

"We're OK with that? No, we shouldn't be," he said.

Baltimore Sun reporter Alison Knezevich contributed to this article.

pwood@baltsun.com

IS IT SAFE TO SWIM?

For those who swim in rivers and the Chesapeake Bay, officials offer the following tips:

•Cover any cuts or wounds with waterproof bandages.

•Wear swim shoes to avoid getting cut on shells or rocks.

•Don't swallow water.

•Shower after swimming and wash your hands before eating.

•Pick up dog waste and dispose of diapers properly.

•Don't swim in areas with high bacteria counts.

•Don't swim within 48 hours of a heavy rainfall.

•Don't feed geese, ducks or other wildlife near beaches.

Resources for finding bacteria levels at Maryland beaches:

•Maryland Department of the Environment: http://www.marylandhealthybeaches.com

•Maryland Department of Natural Resources water safety: mddnr.chesapeakebay.net/eyesonthebay/swim_beach_info.htm