Haverhill Sewer Break – Dangerous Fecal Bacteria Levels Improving in Merrimack River
July 8, 2026 (7:00am). Haverhill, MA – The Merrimack River downstream of the Haverhill sewer main break shows early signs of clearing dangerous bacteria levels with the exception of the mouth of the river. However, Tuesdays’ rain could add bacteria to the river through stormwater runoff. Fortunately, Haverhill did not have a combined sewer overflow (CSO) on Tuesday.
On June 29th, the Merrimack River Watershed Council (MRWC) began testing 7 sites, from Haverhill to the river’s mouth, posting results 24 hours later (due to lab incubation time).
Samples have continued to show unsafe readings at the majority of downstream sites for over a week, with samples taken Monday July 6th being the first time that a majority of sites have tested safe for bacteria. Monday’s two unsafe sites were at the very mouth of the river with unfortunately very high fecal bacteria readings. Salisbury Beach (river side) was 6-7x the safety limit and Plum Island Lighthouse was 4-5x the safety limit. Tuesday’s test results (available by late Wednesday afternoon) will be important to confirm these readings hold true. Wednesday’s test results will be important to identify any impact from Tuesday’s rain.
It is important to stress that these results reflect sampling from Monday and results can change considerably in 24 hours. No one should assume these results can determine whether it is safe or unsafe at these locations today. It is also important to note that these results are from sites within the river and up to where the river meets the ocean.
State testing for beach safety is occurring outside of the river at ocean facing beaches. On Tuesday, the State’s interactive website on beach closures (www.mass.gov/info-details/
Due to the residual impact of the Haverhill sewer line break, MRWC recommends that people do not engage with the Merrimack River at the mouth of the river until further testing can validate that it is safe to do so. MRWC defers to the state for determinations at ocean facing beaches.
Unsafe levels of fecal bacteria can cause gastrointestinal diseases, infections and even death. The levels detected are unsafe for humans and pets. Young people, the elderly and those with compromised immune systems are at greatest risk.
MRWC will continue to post daily test results on its website (www.merrimack.org) until the bacteria levels return to normal. Test results are compared to EPA safety limit and are conducted at MRWC water quality testing sites with several years of historical data.
On Friday, June 26, a sewer main break occurred in Haverhill. As of Wednesday, the City of Haverhill reported that the first of two diversion pipes was installed to keep discharge from going into the river as long as the volume remains under Haverhill’s regular sewer flow. A second diversion pipe was installed over the holiday weekend; however, the new temporary configuration cannot handle the same volume as the original pipe, so sewer discharges from CSOs could be larger and more frequent. Prior to the repair, the overwhelming majority of Haverhill’s sewage was discharged directly into the Merrimack River at an estimated rate of 7-10 million gallons a day.
To understand the impact of the break and the resulting release of raw sewage, it is important to put the discharge into perspective. Haverhill has an average of 35 combined sewer overflow (CSO) events in a year. A median Haverhill CSO discharges roughly 60,000 gallons. However, a large Haverhill CSO (top 2%, or roughly once every 2 years) can discharge approximately 10 million gallons. Typical Haverhill CSOs impact an area immediately downstream for roughly 3 days and do not significantly impact the bacteria levels beyond the Artichoke River in West Newbury. In this context, the sewer main break is a major disruption above and beyond what is typically discharged into the Merrimack River.
There are at least two additional factors to keep in mind when putting this unprecedented event into context. First, the discharge from the sewer main break was 100% sewage, not diluted with stormwater run-off, as is the case during a CSO. Second, this was an ongoing and compounding discharge. Both factors likely make bacteria levels higher and the area of impact larger than a CSO of this magnitude.
While this event is a concern for people and wildlife during the time bacteria levels are elevated, it is not necessarily a long-term catastrophe for the river. This in no way diminishes the current safety and health concerns. It does, however, give hope for the river’s capacity for recovery.
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For more information please contact the Merrimack River Watershed Council.
Curt Rogers, Executive Director: crogers@merrimack.org , (617) 755-1640
Tewksbury PR Partner
These posts are from the great organizations around Tewksbury that provide updates to the Carnation.
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