35th Anniversary logo for Friends of Casco Bay

Up the Watershed; Protecting the Presumpscot protects the Bay


Friends of the Presumpscot River board members Will Plumley (top center) and Michael Shaughnessy (top right) led a walking tour along the river in Westbrook with Friends of Casco Bay in June. Friends of the Presumpscot has been a tireless champion for the river, working to improve water quality, remove dams, restore fish passage, and amplify the stories of Abenaki river stewards.

Friends of Casco Bay is working with Friends of the Presumpscot River and others to better understand water quality in the Presumpscot River, the largest river that flows into Casco Bay. This river drains 648 square miles, approximately two-thirds of the entire Casco Bay watershed. From its headwaters at Sebago Lake, the Presumpscot winds its way more than 25 miles to Portland and Falmouth where it empties into the Bay.

“This magnificent river nourishes the estuary,” says Casco Baykeeper Ivy Frignoca. “We need a healthy Presumpscot to have a healthy Casco Bay.”

Friends of Casco Bay is working to better understand conditions in the lower Presumpscot River, which runs from Saccarappa Falls in Westbrook to head of tide. This segment of the river has Class C status under the Clean Water Act, a lower classification than all other segments of the Presumpscot further upstream.

Staff Scientist Mike Doan and Science and Advocacy Associate Heather Kenyon clean a modified lobster trap containing a data sonde — a scientific device that measures water quality characteristics. The sonde was stationed in the lower Presumpscot River for the summer, above head of tide.

Under the Clean Water Act, bodies of water in Maine are classified as Class AA, A, B, or C based on their health. Class AA and A waters are the healthiest and receive the highest protections. Class C waters allow for some modification to natural conditions caused by human activity, but must still be swimmable, drinkable, and fishable.

This summer, Friends of Casco Bay deployed a data sonde — a scientific device that measures water quality characteristics — in the river to continuously monitor conditions just above head of tide. The Maine Department of Environmental Protection (DEP) deployed a similar sonde to collect data further upstream, above the outfalls of the Sappi paper mill and the Westbrook wastewater treatment plant. Our goal in working with DEP is to see if the lower Presumpscot River’s oxygen levels merit upgrading its Clean Water Act classification from Class C to Class B.

The Presumpscot is the largest river that flows into Casco Bay, draining approximately two thirds of the watershed. This aerial image was taken above Presumpscot Falls on the Portland-Falmouth border, showing the river emptying into the Bay in the distance.

“This summer’s data will be evaluated to help determine whether the lower Presumpscot can be upgraded,” says Ivy. “We are curious and concerned about the effect of summer drought conditions on the river’s health. We are worried that lower flows or higher river temperatures could reduce the amount of oxygen in the water that is available for fish and aquatic life.”

We look forward to sharing what we learned once we, our partners, and other experts analyze the river data from this summer.