Historic mill dams, often featuring picturesque waterfalls and duck-filled impoundment ponds, are a common sight in small-town Massachusetts. Most of the state’s 3,000 dams are obsolete, but they do serve as a connection to a colonial and industrial heritage that is important for many community members.
Advocates of dam removal look back to a time before these barriers blocked the rivers. Once, tens of millions of river herring and other migratory fish traversed New England waterways. They provided sustenance to people and many other species. Dams greatly reduced or eliminated those fish populations. Removing dams reconnects ecosystems upon which fish, wildlife, and people still depend. It also protects communities and infrastructure. Climate change threatens to bring more flooding to the region, which aging dams may not be able to withstand.
NOAA’s Office of Habitat Conservation and its long-time partners the Ipswich River Watershed Association and Massachusetts Division of Marine Fisheries have spent decades trying to restore the Ipswich and Parker River watersheds in the Great Marsh, the state’s most ecologically rich coastal area. Now, with $2.5 million through the Bipartisan Infrastructure Law and Inflation Reduction Act, the project partners finally have the funding to address problematic dams on both rivers.
The project will:
- Remove the Larkin Mill Dam on the Parker River and the South Middleton Dam on the Ipswich River
- Complete the design work and permitting for removal of the Ipswich Mills Dam, the first dam on the Ipswich, which currently blocks tidal flow between the river and the ocean
- Build fishways around the Willowdale Dam on the Ipswich River and Howlett Brook Dam on an Ipswich tributary
- Allow migratory fish including river herring, American eels, and other species to reach historic spawning and rearing grounds
- Reduce flood risks to the community and eliminate expensive maintenance costs and public safety liabilities to towns
NOAA staff have been supporting restoration projects in the watershed for more than 25 years. One of the first community-based restoration projects ever implemented by the NOAA Restoration Center involved the remediation of an undersized culvert blocking tidal water in Ipswich.
“This is the culmination of years and years of research and prioritizing,” says Neil Shea, Restoration Program Director at Ipswich River Watershed Association. “Working with NOAA has been key because their awards are truly cooperative. Their expertise and collaboration makes things go much smoother when challenges come up, as they always do.”
Restoring Fish Populations Means More Food for Everyone
“With a nod to Hemingway, river herring are ‘a movable feast,’” says Ben Gahagan, Diadromous Fish Biologist for the Massachusetts Division of Marine Fisheries. “If you have a successful river herring run, you have millions of small, young fish pouring out of that system in summer and fall. Many commercial ocean species like striped bass, cod, blue fish, and tuna prey on river herring. In the ocean, river herring absorb all these nutrients and bring those back to the rivers in the spring when they return to spawn. In the river, everything eats them, from birds to otters, raccoons, and turtles.”
The Parker and Ipswich Rivers once supported some of the most productive migratory fish runs in Massachusetts. However, the population of river herring dropped dramatically in the Parker River and has been virtually eliminated in the Ipswich River largely due to dams. With dams blocking fish passage on many other New England rivers, the overall loss of biomass flowing into the ocean is tremendous. Elsewhere in the region, researchers have connected the decrease in river herring to the collapse of inshore fisheries like cod.
Every river opened up for river herring adds to the resilience of the coastal food web. This project on the Ipswich and Parker Rivers will open up almost 140 miles of main stem and tributary miles for migratory fish to return.
It will also improve water quality benefiting all wildlife. Removing the dams will decrease temperatures, increase oxygenation, and allow nutrients and sediment to flow into the Great Marsh. Designated as an Area of Critical Environmental Concern, the Great Marsh is the largest continuous salt marsh in New England. It receives special recognition because of its importance for fisheries, bird habitat, and tourism.
“Currently, high tides come up the mouth of the Ipswich River and hit the Ipswich Mills Dam,” says Brian Kelder, NOAA Marine Habitat Restoration Specialist. “By removing the dam, we're giving room for the tidal exchange to migrate up the river which is important from a habitat standpoint. Species like rainbow smelt spawn right at that tidal interface.” Eliminating the Ipswich Mills Dam will restore 1.5 miles of tidal freshwater habitat.
Dam Removals Protect Communities and Infrastructure
Since the beginning, NOAA Marine Habitat Restoration Specialist Eric Hutchins has been building community support and working with dam owners to make the removals a reality. Although not all community members support the removals, many have come to understand the benefits of bringing back a more natural river system.
“I respect the opinions of people who want, for example, to preserve their impoundment pond,” says Hutchins. “If I lived next to the pond I might prefer it too. However, my job is to promote the bigger picture for the greatest benefit for the greatest number of people, and clearly these are good projects for that.”
Taking down the Larkin, South Middleton, and Ipswich Mills Dams will remove the risk of catastrophic flooding for neighboring towns and major roadways. In Massachusetts, data shows that climate change is causing heavier rainfall and intensifying storms. A 2023 report by the Metropolitan Area Planning Council showed that the number of intense, 2-day storms increased by 74 percent from 1901 to 2016. The heaviest rain storms now drop 55 percent more precipitation than the rainiest days of the mid-20th century. Analysis estimates that there will be an additional 40 percent increase by the end of this century.
This puts 100- and 200- year-old dams—which were not designed to hold back such heavy flows—at risk of failing. “This summer was one of the rainiest on record,” says Shea. “In Leominster, Massachusetts, which has a lot of old dams in various states of disrepair, flash flooding from a thunderstorm caused a dam to fail and others came close to failing.”
“If you don't maintain these structures, which is very expensive to do, you're going to have dam failure,” says Gahagan. “This is especially bad for downtown Ipswich because there's a ton of infrastructure—bridges, apartments, and businesses—directly downstream of the Ipswich Mills Dam. If you have a failure, you’ll have all of the floodwaters plus the water in the impoundment pond flowing out. It's a huge liability for the town.”
This year the team finished building a fishway around the Howlett Brook Dam which will allow river herring to reach historic spawning ponds. The partners plan to remove the South Middleton and Larkin Mill Dams in 2024 and 2025, while designing and permitting the removal of the Ipswich Mills Dam. The partners will seek additional funding to demolish the dam and restore healthy flow regimes. NOAA awarded the Ipswich River Watershed Association and the Parker-Ipswich-Essex Rivers Restoration Partnership an additional $1.4 million to remove tidal barriers at road crossings in the Great Marsh. Work on that project will begin next year.
“Thousands of people from Boston and all around go to the Ipswich River and the Great Marsh looking for natural history,” says Hutchins. “Removing these barriers will make it a more beautiful, resilient system. Many people will be educated about the positive impacts of dam removals. We can hopefully get that message out for decades, if not longer.”