February 1, 2023
Annapolis, US 35 F

Swimming Risk in the Chesapeake Bay

Ever wonder if it is safe to swim in the Chesapeake Bay? What are the risks of contracting disease from swimming in the Bay around Annapolis? Summertime is here and water-related activity is increasing — and the perfect time to review what you can get, from where and how to avoid getting any of it.

How to Avoid Getting Sick in the Bay

Of all the rules to live by, the most important is not to swim within 48 hours of a rainfall.  

“Anytime after a significant rainfall… we know the water will be overloaded with bacteria,” according to a former director of environmental health for the Anne Arundel County Health Department.

Annapolitans can avoid Bay related infections by following these 5 simple rules:

  1. Do not swim in the Bay before checking this site:
    Evolve Medical provides primary care and urgent care to Annapolis, Edgewater, Severna Park, Arnold, Davidsonville, Gambrills, Crofton, Waugh Chappell, Stevensville, Pasadena and Glen Burnie.
    Anne Arundel County’s Beach Swimming Guide

    . We are very fortunate to live in one of the best counties (Anne Arundel) in one of the best states (Maryland) for monitoring water quality. In particular, the Anne Arundel County Health Department does an amazing job reporting out areas that are safe or not safe.

  2. After rainfall of 1/2 inch or more, all Anne Arundel County beaches are under a no swimming/no direct water contact advisory for at least 48 hours. Also, do not swim in cloudy, murky water.Evolve Medical provides primary care and urgent care to Annapolis, Edgewater, Severna Park, Arnold, Davidsonville, Gambrills, Crofton, Waugh Chappell, Stevensville, Pasadena and Glen Burnie.
  3. Do not swim in the Bay if you have an ear infection, a perforated eardrum, open cuts, scratches or skin lesions, or a compromised immune system.
  4. Do not swim in water areas where there is a fish kill or where there are any dead animals or known algae bloom.
  5. Try not to swallow water while swimming.

If you follow those 5 simple rules, you lower your risk for getting a water-related disease dramatically.

What Diseases Lurk in the Chesapeake Bay?

The CDC uses the term Recreational water illnesses (RWIs). RWIs are caused by germs spread by swallowing, breathing in mists or aerosols of, or having contact with contaminated water in swimming pools, hot tubs, water parks, water play areas, interactive fountains, lakes, rivers, or oceans. (RWIs can also be caused by chemicals in the water or chemicals that evaporate from the water and cause indoor air quality problems.) RWIs can be a wide variety of infections, including intestinal, skin, ear, lungs, eye, nervous system and wound infections.

The most commonly reported RWI is diarrhea. Diarrheal illnesses can be caused by germs such as Crypto (short for Cryptosporidium), Giardia, Shigella, norovirus and E. coli O157:H7.

In 2009, the Chesapeake Bay Foundation published, “Bad Water: The Impact on Human Health in the Chesapeake Bay Region” (which is a good resource). In it, CBF states, “The Chesapeake Bay in summer is like a warm pond with a broth of nutrients at the right temperature to breed algae and bacteria.” 

Vibrio (“Flesh Eating Bacteria”)

Otherwise known as “Flesh-eating bacteria,”, there are several species of Vibrio. Vibrio vulnificus causes severe skin ulcers, gangrene, and deadly blood infections in people who expose cuts to warm saltwater containing the bacteria, as well as diarrheal illnesses in people who eat shellfish infected with Vibrio.

Another species, Vibrio parahaemolyticus, causes diarrhea, vomiting, and skin infections, but is seldom deadly.

The best known is Vibrio cholerae which causes cholera, a diarrheal disease now virtually eliminated from the United States.

Harmful Algal Blooms and Cyanobacteria

One toxin-producing form of algae, called blue-green algae, is not really algae at all, but rather a class of bacteria, called cyanobacteria. There are at least 35 types of algae in the Chesapeake Bay that produce toxins. The most well known, Blue-green (Microcystis), is the cause of most blooms and fish kills reported.

A 2008 study reported that between 2000 and 2006, 31 percent of the waters tested with blue-green algal (cyanobacteria) blooms had enough toxins to make them unsafe for children to swim in.

According to the World Health Organization, Cyanobacterial toxins are classified by how they affect the human body. Some will affect the liver, nervous system or intestinal systems. Some symptoms can include skin irritation, stomach cramps, vomiting, nausea, diarrhea, fever, sore throat, headache, muscle and joint pain, blisters of the mouth and liver damage. Swimmers in water containing cyanobacterial toxins may suffer allergic reactions, such as asthma, eye irritation, rashes, and blisters around the mouth and nose.

Mycobacterium marinum (M. Marinum)

This infection can require 6 months of antibiotics and usually happens to people who swim with an open skin cut. The average time between being in the water and showing signs of infection was 21 days (but the range was anywhere from 5 to 270 days). Also known as “Fish Tank Granulomas,” they are slow growing and typically affect the elbows, knees, and backs of feet and hands. The infection can look like either nodules (image left) or shallow ulcers (image right).


A protozoan organism comes from human and animal poop. Cryptosporidium can cause diarrhea, and in people with compromised immune systems, more serious illnesses.  Dr. Thaddeus Graczyk, a Johns Hopkins Bloomberg School of Public Health researcher, found Cryptosporidium (which local health departments do not test for) at levels that could infect people in 70 percent of weekend samples at a Baltimore County beach.

On the other hand, the Maryland Department of the Environment has said that testing for Cryptosporidium is impractical and expensive.  Instead, checking for other signs of fecal contamination in general such as a simple test for E. coli or Enterococci bacteria is reliable. These tests are performed by local health departments, follow guidelines set up by the EPA, and use a conservative estimate of risk. 


A compound in polluted runoff from farms, lawns, and streets, nitrates seep into surface and ground water. Drinking water with excessive nitrates can potentially raise the risk of cancer, nervous system deformities in infants, hemorrhaging of the spleen, and other problems.

If you have any questions or have been experiencing one of the above symptoms, see your primary care physician immediately. Evolve Medical is also happy to see you. Same day scheduling on-line here or call 844-322-4222. Or email them at [email protected].

If you find these health and wellness updates helpful, follow Evolve Medical on Facebook, Twitter, Instagram or Google+.

Evolve Medical provides primary care and urgent care to Annapolis, Severna Park, Arnold, Davidsonville, Gambrills, Crofton, Edgewater, Pasadena and Glen Burnie.
Evolve Medical provides primary care and urgent care to Annapolis, Edgewater, Severna Park, Arnold, Davidsonville, Gambrills, Crofton, Waugh Chapel, Stevensville, Pasadena and Glen Burnie.
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  1. It seems like this would be more useful if we knew how many Bay swimmers get these during the entire summer.

    Almost as though this isn’t much of a problem.

  2. Is there a website where we could look up more locations nationally? Might also come in handy on vacation.

  3. If the water was a danger, the committee would not let people swim….final. The bay swim is harmless because it is early in the season where the water is still cool enough. Just swim, you’ll never regret it! I certainly did and it was awesome!!!!

  4. I’m shocked to read this article only days after learning a FB friend lost her father 5 days after crabbing in the bay near Annapolis last week! He cut his toe in the water then very quickly lost his life to vibrio. This is not only real it’s a tragic, scary, painful and preventable way to die. This article was published 23 days before his rather routine day in the bay. People think this can’t or won’t happen to them, but I’m here to tell you to pay attention and pay heed. Please read and share! I still can’t believe you can die from just being in the water, but as an ear witness, it’s closer to home than you think!

  5. My friends’ father lost his life last Thursday after crabbing in the bay near Annapolis, something he did routinely. He cut is foot in the water and within 5 days he passed away after contracting the skin eating disease vibrio mentioned in the article. It’s is very true! Please search google articles for actual incidents then tell me if you would still allow your children to swim in the bay. The article is a warning, denial is a choice… Choose wisely as the consequences are not reversible.

  6. I am really sorry to hear this.
    I was born in Dundalk Md. and grew up on the Back River when it was Blue and sandy….marine life was abundant. Turtles, blue crabs (large), Perch, Carp, birds of all types….it was beautiful paradise then.
    Lived at 3706 Edgewater Place
    All us kids grew up loving our river getting to watch Cox Point boat races.Then in 60s my father fought against the sewage treatment facility with many others….and lost.
    Years later went back by boat..jumped into the water and sunk up to almost my hips in black oozing sludge….water was foul smelling like raw sewage….no fish, few birds..
    I was sorry for even going back to see my old place.
    I knew between the sewage plants, fertilisers, herbicides that soon the Chesapeake was as we know it was going to be destroyed. Power, greed, money, humans destroying the Earth that we wanted to leave to generations of our family in the future. Sadly it does not look good at all.

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