Bacteria in Our Waterways


Streams can be a fun and exciting place to explore and understand nature, but all natural waters contain algae, bacteria, viruses, and parasites. Bacteria are common single celled organisms that occur in natural waters across the world. Most bacteria are harmless, but some can potentially cause Illnesses in humans and pets.

During a heavy rainfall, pollution from the land washes into rivers, lakes and streams. This pollution sometimes contains fecal indicator bacteria (FIB). These non-disease causing bacteria come from warm blooded animals (sometimes humans) and can multiply readily under the right conditions. High levels of these indicator bacteria do not necessarily mean the water is unsafe, but caution should be taken.

Little Falls Stream


Potential Illnesses

The presence of E. coli and Enterococci bacteria (fecal indicator bacteria) can be an indication of fecal pollution, which may come from stormwater runoff, pets, wildlife, and human sewage. All natural bodies of water contain microscopic organisms including fecal bacteria and parasites that cause gastro-intestinal illness in people.

Escherichia coli (E. coli) and Enterococci bacteria normally live in the intestines of healthy people and warm-blooded animals. Most types of E. coli are harmless or cause minor illness, but a few strains, can cause more severe symptoms. Most water-related illnesses are minor for people in good health. They typically require little or no treatment and have no long-term health effects.

When FIB bacteria levels exceed the established criteria, risk of illness due to microorganism exposure increases. FIB also indicate potential exposure to other microbes including Giardia, Cryptosporidia, and other protozoa.

Common Illnesses

The most common health implications or illness associated with contaminated water include:

  • gastroenteritis (nausea, vomiting, headache, stomachache, fever and diarrhea)
  • ear, nose, and throat infections
  • rashes
  • wound infections through an open cut or wound

Keep in mind that contaminants can find their way into all waterways, so there is always a risk for infections, especially for those who have chronic illnesses.

Stay Safe!

To mitigate the public health threat it is recommended that residents should:

  • Avoid physical contact with the stream water
  • Avoid wading in the water
  • Keep pets out of the water
  • Avoid drinking stream water or touching stream water
  • Wash hands should physical contact occur and before eating
  • Avoid water contacting an open cut, wound or skin infection
  • Pay attention and follow advisory signs

Visit the Maryland Department of the Environment for Maryland water quality standards.



A warning sign may be posted advising the public that the water may be unsafe for recreation such as swimming, wading, or skin contact. This includes pets! Pay attention to warning signs when they are posted—they will keep you and your pets safe and healthy.

Warning - Bacteria in Waterways


Willett Branch

Willett Branch Signage Map Due to high levels of E. coli detected in Willett Branch along with bacteria source tracking indicating a potential human source, the Montgomery County Department of Health and Human Services has requested that Montgomery Parks post warning signs along Willet Branch to the confluence with Little Falls. E. coli are indicator bacteria indicating fecal contamination and the possible presence of disease-causing organisms.


Protect Our Waterways!

Here are some suggestions to help keep yourself and our waterways safe:

  • Do not feed wildlife
  • Dispose of trash and recycling in appropriate containers
  • Don't dump household chemicals or wastes in street drains
  • Avoid using excess fertilizers or pesticides on your yard
  • Pick up pet waste
  • Maintain your septic system
  • Report possible sources of contamination to MC311 (240-777-0311)