Bacteria Health & Safety

OARS is attempting to answer this with our E. coli bacteria monitoring program. Bacteria and other pathogens can enter the rivers from leaking sewers or septic systems, stormwater runoff, or wildlife or dog waste. The EPA has linked high levels of E. coli (an indicator bacteria) in swimming water to high rates of gastrointestinal illness.

Our bacteria monitoring efforts help keep the Sudbury, Assabet, and Concord rivers safe for recreation and wildlife. This dashboard provides up-to-date results from our regular water sampling, showing bacteria levels across key locations in the watershed. Use this interactive tool to check water quality conditions before swimming, fishing, or paddling, and stay informed about the health of your rivers.

VIEW DASHBOARD ON SEPERATE WEBPAGE

OARS volunteers collect river water samples bi-weekly between May and September at six locations throughout the river system. The samples are then analyzed in a lab, and the counts of E. coli bacteria are recorded as the Most Probable Number (MPN) of colony-forming units (cfu). The EPA has established swimming safety thresholds of 235 cfu/100mL for single samples or 126 cfu/100mL for seasonal geo-mean averages. We intend to use our sampling results to determine which river sections are safe for swimming and to identify pollution sources to track and eliminate them. Please refer to the attached Bacteria Monitoring Summary for more details.

2023 Bacteria Monitoring Results

Our 2023 bacteria monitoring highlighted the same sites of concern as in previous years. The Ashland, Lowell, and Maynard sites all had seasonal geometric means above the 126 CFU/100 ml swimming threshold. The Hudson site also exceeded this threshold in 2023. The year 2023 was a wet-weather year. Hudson has a history of low bacteria levels in dry weather and high bacteria levels in wet weather, indicating a dominance of storm-water surface pollution.

The two new sites, Carter Avenue in Billerica and Little Farms Road in Framingham continued to have low levels of bacteria. Carter Avenue is very similar to the Bedford Route 225 site we previously monitored. Both Carter Avenue and Route 225 have perfect records with no exceedances of the BAV threshold. Both sites are within the Wild & Scenic segment of the Concord River. Little Farms Road is very similar to the Wayland Route 20 site that we previously monitored. These two sites have very rare BAV exceedances, limited to significant precipitation events. Both sites are within the Wild & Scenic segment of the Sudbury River.

The following table summarizes the 2023 results for E.coli bacteria at our six core monitoring sites in the Sudbury, Assabet, and Concord rivers.

Results (May 15, 2023–Spetember 11, 2023)

Site#	Description	River	Samples	Exceed-ances	% Exceeded	2023 Geo-Mean	2022 Geo-Mean	2021 Geo-Mean	2020 Geo-Mean	2019 Geo-Mean
ABT-007	USGS gauge, Maynard	Assabet	9	4	44%	195	193	164	289	121
ABT-162	Cox Street, Hudson	Assabet	9	4	44%	173	123	119	203	161
CND-009	Rogers Street Bridge, Lowell	Concord	9	3	33%	191	203	153	216	147
CND-093	Route 4 Carter Avenue, Billerica	Concord	9	0	0%	51	9
RVM-001	Lawrence Street, Lowell	River Meadow	9	8	89%	502	504	417	427
SUD-137	Littel Farmd Road, Framingham	Sudbury	9	2	22%	121	102
SUD-236	Route 135, Ashland	Sudbury	9	2	22%	186	201	169	348	151

* Cells shaded orange exceeded the single-sample threshold more than 25% of the time or the geo-mean threshold for the year

2023

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2022

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2021

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Older Summaries

Volunteers have also helped us conduct special studies for source-tracking bacteria in locations of concern. Between 2020 and 2022, we conducted intensive research in Lowell to track sources of bacteria pollution in the lower Concord River. In 2023, we conducted a study in Maynard to track sources of bacteria pollution in the Assabet River. In 2024, we plan to conduct a similar study in Ashland to identify sources there.