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Blue Water

Tidal Waters Monitoring Program
Spring & Summer 2023

begins May 25th!

The information on this page, and accompanying alerts, are provided as a public service by Assateague Coastal Trust and the Assateague COASTKEEPER. We publish bacteria sample results (enterococcus), and the results of Worcester County’s official advisories on Swim Guide each week. Download the Swim Guide app HERE. Scroll down on this page to view the latest water quality indicators and sample results as well as more information. The Assateague Coastal Trust Tidal Waters Monitoring Program begins May 25, 2023!

Only the State authorized County Health Department or Environmental Programs agencies can issue a Swimming Advisory. The Swim Guide App is to be used for guidance only. 

Why Bacteria?

The presence of enterococcus in waterways can be harmful to human health

Enterococci are bacteria that live in the intestinal tracts of warm-blooded animals, including humans, and therefore indicate possible contamination of streams and rivers by fecal waste. Sources of fecal indicator bacteria such as enterococci include wastewater treatment plant effluent, sewage discharged or dumped from recreational boats, leaking septic systems, stormwater runoff, domestic animal and wildlife waste, improper land application of manure or sewage, and runoff from manure storage areas, pastures, and feedlots. There are also natural, non-fecal sources of fecal indicator bacteria, including plants, sand, soil and sediments, that contribute to a certain background level in waterways and vary based on local environmental and meteorological conditions.


is it safe to swim?


The EPA recommended cut-off for enterococcus bacteria levels is 104cfu/mL. Samples exhibiting 105 cfu/mL of bacteria units per 100 mL sample or higher are also displayed as red swimmer icons on the Swim Guide app and red circles in Water Reporter.

Don’t swim after a rainstorm. The general rule is to wait 48 hours after a precipitation event.

  • Wash off with warm water and soap after recreating in on or around waterways.

  • Don’t swim where there are posted beach closings or advisories.

  • Don’t swim if you have open cuts, sores, or scratches.

  • If you have an impaired immune system, check with your doctor about swimming in the coastal bays.

  • If you notice a particularly red, swollen or blistered skin infection after swimming in bay water, seek qualified medical help immediately.

  • If you develop gastrointestinal disease symptoms after swimming in the bay or eating shellfish, seek immediate medical treatment.

Bacteria samples (enterococcus) are sampled at each site, once per week (generally on Thursdays). Sample results are made available to the public 24 hours following the day samples were collected. You can check results on the COASTKEEPER Facebook page, or on the Swim Guide or Water Reporter apps.

Water quality indicators and sample results reflect conditions at the time which data and samples were collected. It is important to note that certain water quality indicators can, and often do change daily. Precipitation events in the watershed can result in urban and agricultural runoff, which can impact the water quality of area waterways. It is important to monitor local water quality in conjunction with weather patterns.

*DNS indicates a sample was not collected or no data is available.

We test for more than bacteria

We also share our water quality data in addition to the bacteria results. Every week we are also measuring parameters such as pH, dissolved oxygen, turbidity, and conductivity in our 11 sites around the coastal bays. You can check them using the button to the right

Water Pollution
Sea Pollution
Footprints on Sand

Water Quality Questions Or Concerns?

If you have questions regarding our

Tidal Waters Monitoring Program, concerns about water quality in local waterways, or need to report pollution, please contact

Assateague Coastkeeper at




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