Gunpowder River Water Quality Update August 1st, 2023

Gunpowder Riverkeeper is proud to provide up-to-date water quality information to residents of Baltimore and Harford counties along the Gunpowder and Bush River Watersheds. 

For a map based on Bacteria Monitoring Results and more information on this monitoring work, please visit:

In partnership with Community Environmental Laboratories, an EPA-certified water testing laboratory located in Harford County, we have the capacity to sample various access points along the river for their respective E. Coli levels. Our water monitoring results help inform the public on where they can recreate safely along the River and provide indicators for possible stormwater or point-source pollution. 

The EPA’s Safe Swimming Criteria for Maximum Probable number of E. Coli is 126 MPN (geometric mean) and 235 MPN (single sample).

On August 1st 2023, Gunpowder Riverkeeper sampled at 5 locations along the Gunpowder River Watershed including; Monkton (Monkton Rd/Rt. 138), Pot Rocks (Belair Rd/Rt 1), Jericho Bridge at Little Gunpowder (Jerusalem Mill) Town Creek and Foster’s Branch (Mariner’s Point Park).

We sampled in dry conditions with less than one inch of rainfall in the preceeding 48 hours. MDE advises against swimming in the river within 48 hours of a 1 inch rainfall event

We’ve outlined our results and pictures from our sample sites below: 

Monkton – 300 MPN

Pot Rocks Bel Air Rd/ Rt 1. – 70 MPN

Jericho Bridge – 130 MPN 

Town Creek – 500 MPN 

Foster’s Branch – 22 MPN

According to the Maryland Department of the Environment’s fact sheet on the EPA’s water quality criteria, at the EPA’s Safe Swimming threshold of 126 MPN (geometric mean) / 235 MPN (single sample), it is estimated that 36 individuals out of 1000 swimmers may contract a water-borne gastroenteritis illness. 

When our samples indicate E.Coli counts over the EPA’s criteria, it is recommended that the public avoid contact with the water within that area of the Gunpowder River until further sampling is conducted. The Maryland Department of the Environment also advises to avoid swimming in the river within 48 hours of a heavy rainfall event. For more advised precautions, see the Department’s tips for swimmers

For additional water quality monitoring in the Gunpowder, Little Gunpowder, Bird, Middle River and Bush Watersheds:

Harford County Health Department Recreational Water Sampling

Baltimore County Department of Health Water Sampling 

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