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Pollution is threatening Cape Cod’s famous waters. Its towns are spending hundreds of millions to head off an environmental disaster.

On Cape Cod, poorly maintained and aging septic systems are a primary cause of the nitrogen pollution that plagues coastal ecosystems. The deteriorating water quality is causing people to lose out on recreational and commercial opportunities like swimming, shellfishing, and fishing.Jonathan Wiggs/Globe Staff

BARNSTABLE — The beauty of its placid bays, estuaries, and ponds draws millions of visitors to Cape Cod each year. But deteriorating water quality is threatening the environmental and economic future of the tourist mecca.

About 90 percent of the Cape’s estuaries — important for marine life and recreation — had unacceptable quality in 2022, according to a recent report from a local conservation organization. The main culprit: decades of nitrogen pollution, primarily from septic systems.

Most Cape towns are planning new waste water systems that would improve water quality, but it could take decades to complete them and for the nitrogen already in the ecosystem to flush out. That reality is setting in among local leaders, environmental groups, and residents.


“It may be worse before it gets better,” said Richard Delaney, chief executive of the Center for Coastal Studies in Provincetown. “But the correction, the solution, is underway.”

Towns have recently been making progress. Mashpee is building the first phase of a new waste water treatment plant — set for completion in late spring or early summer 2024 — that initially will connect to homes on 20 roads, about 5 percent of all households, for an estimated cost of $54 million.

After the end of a planned partnership among Yarmouth, Dennis, and Harwich, the towns are now moving forward individually. Yarmouth has set out a 40-year plan to create a centralized waste water treatment plant that will bring direct sewer connections to properties along densely populated Route 28 and Old Main Street. The first phase of that project alone will cost an estimated $207 million.

As the largest community on the Cape, Barnstable has a massive undertaking to bring sewer service to property owners: a $1.4 billion project that will take 30 years to complete. The first phase for roughly 90 miles of sewer infrastructure is underway. Once complete, the initial portion of the project will remove nearly half of the nitrogen polluting the town’s waters, according to projections.


But after four years of construction, residents in Barnstable already are expressing fatigue, said Town Manager Mark Ells.

“They’re like, ‘When is this going to be done?’” Ells said. “And I’ll say, ‘26 years from now,’ and they’ll just look at me.”

It takes so long because planning, permitting, developing, and securing funding for projects to connect thousands of homes to sewer systems takes time in a heavily developed community such as Barnstable, Ells said. The sewers are going into where people live, where buses pick up children, where police officers and firetrucks need to navigate. And the tourists pour in during the summer.

For dense areas, replacing septic systems is critical. They account for 80 percent of the nitrogen entering the Cape’s watershed, according to the Cape Cod Commission, a regional land-use planning, economic development, and regulatory agency.

Nitrogen influx destroys animal habitats and violates water quality standards for estuaries, ponds, and groundwater. The deteriorating water quality is causing people to lose out on recreational and commercial opportunities such as swimming, shellfishing, and fishing.

Following the passage of the Clean Water Act in 1972, federal funds were available to implement large waste water projects. However, towns on the Cape declined. Residents feared that if sewers were built, the region would become overdeveloped. (Development happened anyway.)


“It was a decision that really served the Cape poorly,” said Andrew Gottlieb, executive director of the Association to Preserve Cape Cod, which issued the recent water qualify report.

Without centralized waste water facilities and with large-lot zoning to discourage density, the critical habitats and the landscape became fragmented by housing with space-consuming septic systems. Gottlieb said this contributed not only to poor water quality but also to other problems the Cape faces today, including unaffordable housing.

By 2015, only 3 percent of Cape Cod land had public waste water treatment infrastructure: small parts of Provincetown, Chatham, Barnstable, and Falmouth.

But the work has been accelerating of late. Bourne opened a Buzzards Bay treatment plant in 2021 that services commercial areas. Falmouth is expanding its waste water infrastructure piece by piece. The current system covers 11 percent of developed properties, and the town plans to expand to the Great Pond area.

Other towns, such as Eastham and Wellfleet, are developing smaller plans.

“A lot has happened,” Gottlieb said. “It’s been a long time coming. We’ve been screwing up this resource, for a long time.”

Residents will be assessed various fees and surcharges on property taxes to help fund the new systems. The cost will vary depending on the property and from town to town; in Barnstable, for example, the average cost of connecting to the system is estimated at $17,000, and there is a separate assessment that the town will cap at $10,000.


There is a state tax credit and various loan programs to help property owners manage the cost.

Towns also receive low-interest loans from the state, as well as subsidies under the 2018 law commonly known as the Airbnb tax, which adds a 2.75 percent surtax on overnight stays.

Cape towns received a recent push from the state. The Department of Environmental Protection imposed new permitting regulations in watersheds that went into effect July 7. The 20-year plan allows communities to design and implement waste water solutions tailored to their individual needs to reduce nitrogen pollution.

Barnstable Clean Water Coalition installed a KleanTu septic system in the Sandy Shores neighborhood around Shubael Pond last year. Jonathan Wiggs/Globe Staff

Communities have two years to opt into a permitting process. If they don’t, new septic systems in the watershed would be required to include enhanced nitrogen-reducing technology, and homeowners would be on the hook to upgrade existing systems within five years.

“It’ll force those towns to move quicker on those plans than they may have originally thought,” said Brian Baumgaertel, a senior environmental specialist at the Barnstable County Department of Health and Environment.

In the meantime, the solution doesn’t have to be all sewer. Newer septic systems remove more nitrogen pollution, Baumgaertel said. Other mitigation efforts include shellfish aquaculture, improving wetland functions, and dredging.

Paul Niedzwiecki, chief executive of the Cape Cod Chamber of Commerce, said the No. 1 challenge for the Cape is not convincing towns to do the right thing, or even necessarily finding the money; it’s the execution.

“It’s a priority of the business community. I think all the towns understand the potential risks to the economy and that we have to protect our environment,” Niedzwiecki said. “I think we will make a lot of progress over the next five to 10 years.”