BOSTON — Tens of millions of gallons of untreated sewage have poured into the Merrimack River amid record rains, as recently as this past weekend.

The Greater Lawrence Sanitary District — which treats sewage from Lawrence, Methuen, Andover, North Andover, Dracut and Salem, New Hampshire — has released about 30 million gallons of stormwater and sewage into the river so far this month, according to the Merrimack River Watershed Council, which monitors the discharges.

That’s about half of what the system usually releases into the river in a given year, the group said.

Data on discharges from other treatment systems along the river, including those in Lowell and Haverhill, haven’t been made public, but the river’s advocates say they expect record amounts of effluent spills amid the heavy rains.

“There’s been an enormous amount of sewage and stormwater going into the river,” said John Macone, the council’s policy and education coordinator. “We’ve heard anecdotally from boaters about how brown water is, that there’s been a lot of dead fish, and a really bad stench along certain segments of the river.”

Over the past weekend, the council posted an alert of at least three releases into the river due to heavy rain Sunday.

More than 68,000 gallons of sewage and stormwater were dumped into the river by the Haverhill treatment system between 4:35 and 5:25 a.m., according to the council.

A release from the Lowell treatment system was logged between 5:15 and 6:38 a.m., while the Greater Lawrence district reported a 45-minute discharge at roughly the same time.

The sewage and stormwater comes from dozens of overflow pipes along the river that are part of decades-old treatment systems designed to overflow when inundated, usually because of heavy rain.

The “combined sewer overflows,” or CSOs, violate the federal Clean Water Act but the sewage treatment districts, which predate the law, operate under consent agreements with the U.S. Environmental Protection Agency.

In the meantime, this month is already the rainiest on record in some parts of Massachusetts. The 12.67 inches of rain measured in Worcester in July washed away the old record of 11.24 inches set in 1938, according to the National Weather Service.

As of yesterday, Logan Airport had recorded 9.39 inches of rain so far in July, which is still short of the record from 1921 of 11.25 inches.

Last year, five sewage systems along the 117-mile Merrimack River reported hundreds of discharges, according to data compiled by environmental activists and regulators. Sewage treatment plants located in New Hampshire also contribute to the problem.

Treatment system operators along the river have been pursuing upgrades to curb discharges. They point out that the discharges are but a tiny fraction of the tens of billions of gallons of sewage treated every year and are typically diluted in the wide, fast-moving river.

But environmentalists say large and frequent overflows pose health risks to those who use the river for boating and swimming, as well as communities that draw drinking water. An estimated 600,000 people receive drinking water from the Merrimack River.

A 2015 study published in the journal Environmental Health Perspective found a significant increase in people visiting hospital emergency rooms with gastrointestinal illnesses following raw sewage discharges into the river in the Lowell, Andover and Lawrence area.

Raw sewage also causes algae blooms, which can be toxic to people and deprive water bodies of oxygen, killing fish and other marine life.

Earlier this year, the Legislature passed a bill requiring stepped-up notices of the discharges along the river to let communities know when the water may not be safe.

Lawmakers are considering a plan from Gov. Charlie Baker to spend a portion of the state’s $5.3 billion in pandemic relief funding on projects aimed at fixing the CSO problem.

Baker wants to use about $400 million of that money for water and sewer infrastructure upgrades, including work that would cap CSOs along the Merrimack River. On Tuesday, lawmakers are to hold the first of several public hearings to discuss plans to spend the money.

The Watershed Council supports Baker’s plan and is encouraging its members to write to their lawmakers to seek their approval.

“We think the governor’s plan is good and hope the Legislature will support it,” Macone said. “These rain events are going to become more frequent with climate change, so we need to take steps to improve the long-term health of the river.”

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. 

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