St. Croix River Dam Removal to Bring Fishery Benefits

New Brunswick Power began removing the Milltown Dam this summer, located near Calais, Maine, and St. Stephen, New Brunswick. The work started in July after the company received the required permits from both countries and completed environmental assessment processes and reviews by the IJC and its International St. Croix River Watershed Board.

“This should open an important stretch of the international St. Croix River to ocean-run fish who spawn in freshwater streams,” said Sean Ledwin, a watershed board member.

Milltown Dam is a hydroelectric dam first built in 1881. The dam generates small quantities of power and it would be expensive to make necessary upgrades, New Brunswick Power says. As a result, the company began plans to decommission the dam in 2019.

The company received its final approvals in the spring of 2023 following years of study and public comments from both sides of the river. These included an environmental impact assessment from New Brunswick, a permit from the Maine Department of Environmental Protection, a general permit and project works notification from the US Army Corps of Engineers, and an IJC letter of approval.

Decommissioning

At the watershed board’s June 5 meeting, John Murphy, speaking for decommissioning contractor Pennecon Heavy Civil Limited, said work would commence once the annual alewife and shad run had concluded in July. The work got underway July 1 and is expected to be complete in April 2024.

As a first step, the gated spillway on the US side of the river was removed to allow water to continue flowing out of the St. Croix while the other portions are dewatered and removed. After the powerhouse and spillways are removed, Murphy said substrate and refuge boulders would be placed where the dam was located to help adjust the flow so that fish can safely and effectively swim upstream in a range of conditions. The Milltown Dam is located on the site of the former Salmon Falls, but it’s likely that there have been changes to the river bottom from the dam’s construction, which impact fish habitat, he said.

“The goal is to emulate what it would look like after decades of erosion, (by) using a mix of materials,” Murphy said.

Ledwin said that once the dam is removed, there will be a 16-kilometer (10-mile) stretch of the river where fish can swim freely before reaching the next dam on the system: the Woodland Dam.

But even with the Woodland and Grand Falls Dam further upstream creating obstacles for fish making their way inland to spawn, Milltown’s removal will be a boon for native fish such as alewives, shad, blueback herring and sea lamprey that have struggled to get past its fishway.

Each time fish navigate past a dam and fishway, they use more energy than swimming through an open waterway. This naturally will stop some fish from moving upstream, and there is an increased risk of injury or death for fish moving back downstream, Ledwin explained. As a result, removing Milltown Dam should bring benefits in terms of the number of fish moving past Woodland and Grand Falls dams as it will allow fish to freely move past its former location in both directions.

Milltown Dam’s removal also will adjust how water moves through the lower reaches of the river. Since water will be able to flow through unimpeded, that stretch of the river should be colder than it has been with the dam in place. This should benefit the fishery, particularly given warming trends for the river due to climate change.

“It’ll be a more riverine system,” Ledwin said. “A lot of predators like bass and other things will still do fine in the rivers, but they’ll have less of an opportunity to predate on all the native fish with less stagnant flow.”

A map showing the location of the Milltown Dam within the St. Croix River watershed. Credit: International St. Croix River Watershed Board

Monitoring and Improvements

To keep an eye on conditions after the dam’s removal, including fish passage through the old dam site, Ledwin said s Institute will collaborate with the Passamaquoddy Tribes on the US side of the St. Croix and the Peskotomuhkati Nation on the Canadian side to tag and monitor how fish are using and moving through the newly restored river. This work begins this year and will run for five years, Ledwin said. Separately, the IJC is funding a remote fish tracking project through its watershed board and the St. Croix International Waterway Commission.

Beyond Milltown Dam

There also are fundraising efforts underway to replace outdated fish passage systems on the Woodland and Grand Falls dams with modern ones that are safer, less exhausting and more effective for a wider range of species.

Ledwin said the first focus is on the Woodland Dam, where a fish elevator design is under consideration. Ledwin estimates that fully implementing this new fish passage system will cost at least US$20 million. Private grants and US federal funds have already raised about two-thirds of the cost, he added, with Maine Department of Marine Resources and its collaborators working to raise the remaining funds. If funding allows, work would begin in late 2024. A new fish passageway at Grand Falls Dam, meanwhile, is in the early stages of design and fundraising.

“The Milltown Dam removal and the improvements in passage at the other two dams will result in an extremely large run of river herring (alewives and blueback herring), probably the biggest runs in North America,” Ledwin said. “It will improve runs for shad, sea lamprey and other native fish species, as well as upstream and downstream passage for American eel, which is an important and lucrative fishery in Maine."

With the removal of Milltown Dam and new fish passage being considered at Woodland and Grand Falls,  Ledwin said the Bay of Fundy, which the St. Croix empties into, could see hundreds of millions of juvenile alewives annually, providing food for predators such as puffins, whales and raptors as well as bait for the lobster industry. Alewives also have historically been eaten by people in the St. Croix River basin, making these potential massive runs beneficial for subsistence fishing.

With additional stocking and management programs, it’s possible that Atlantic salmon may even return to the St. Croix with that degree of habitat connection, Ledwin said. All those possibilities start with the decommissioning of the Milltown Dam.