FISH MIGRATION / ALEWIVES

Overview

Mill Brook supports the largest fish migration from Casco Bay. In late May each year, alewives, a type of river herring, enter the Presumpscot River from Casco Bay, then swim up Mill Brook until they reach Highland Lake, their native spawning ground. The journey is almost 11 miles long, and the migration lasts from two to three weeks. About 70,000 fish traveled this route in 2019. In late summer, adult and new juvenile alewives travel back down the Brook in their return trip to the ocean. Adult alewives can make this round-trip three to four times in their lives.

Guided Alewife Walks

Presumpscot Regional Land Trust partners with organizations like the Gulf of Maine Research Institute to host guided educational walks each spring, highlighting the incredible fish migration in our region. Stay tuned for the full video of the Alewife Migration Walk, coming in spring 2025!

Alewife Migration Lecture

Please see below for a video of Dr. Karen Wilson’s, University of Maine, talk on alewives in winter 2021:

The protection of the Mill Brook Preserve, along with our Water Stewards program, ensure that these migration waters remain clean and provide excellent habitat for alewives and the countless other plants and animals in and around the Brook.

Digital Alewife guide

For a downloadable FREE guide about the Alewife and how to view them click the link below. The guide was designed in collaboration with the Gulf of Maine Research Institute and provides information and guidance about the Alewife Migration, detailed information about Alewife, viewing protocol, and more. To download your free guide today simply click  here.

The Gulf of Maine Research Institute (GMRI) has been involved in research and monitoring efforts of alewife for 10+ years and we are proud to partner withGMRI annually on s educational guided walks t around the Alewife Migration.

Mill Brook Alewife Migration Featured in National Geographic!

You know who else thinks that this migration is spectacular? National Geographic. Photojournalist Brian Skerry describes his experience witnessing the alewife run at Mill Brook in this National Geographic article. Don’t miss it!

What is the Land Trust's role in the fish migration, and how can I help?

As the stewards of the largest fish migration from Casco Bay, we have over 50 volunteers involved in ensuring the success of the alfewives’ journey from Casco Bay to Highland Lake, where they spawn.  Member support is what makes this happen; if you are already a member, thank you, if not, please consider taking a minute to join now online, and you too can be a part of supporting this incredible migration.

Volunteer during the Fish Migration

Fish Count Volunteers

We are working in collaboration with USM and the Department of Marine Resources to support ongoing research on the largest fish migration from Casco Bay. You can support these efforts by becoming a Fish Count volunteer. Volunteers count fish as they enter Highland Lake in Westbrook for 30 minute at a time mid-May to early June. Sign up to volunteer for the 2024 season here, and if you have questions please email toby@prlt.org

Fish Migration Ambassadors

Mill Brook supports the largest migratory fish run in Casco Bay, as alewife travel from the ocean through Presumpscot River then Mill Brook to Highland Lake. There are now thousands of visitors who come to see the fish migration at our Mill Brook Preserve. As a result, we have started a new fish migration ambassador program. Ambassadors engage with visitors at the two fish viewing pools, welcoming visitors, answering questions and supporting a successful fish migration. No prior skills are needed and we will provide training. Sign up to volunteer for the 2024 season here, and if you have questions please email toby@prlt.org

For more volunteer opportunities visit our Get Involved page of the website.

When and How to View the Fish:

The fish migrate from mid-May to early June.

Parking and how to get to the fish viewing pools in Mill Brook Preserve:

  • Can I see the fish migration from every one of the Mill Brook Preserve trailheads?

  • Which trailhead is closest?

    • The trailheads on Perry Court and just north of 789 Methodist Road are the shortest hikes to the southern fish viewing pool. Please park safely off the road and completely off the pavement along Methodist Road.

  • Which viewing pool is the best?

    • They are all wonderful but the southern fish viewing pool is the more likely place to see fish. The northern fish viewing pool is more remote, and if the timing is right, you can watch multiple fish ascending the waterfall at once.

  • What can I do to be a good neighbor?

    • All trailheads have limited parking; please be sure not to block driveways or park on neighbors' lawns, and please try and visit during off-peak hours. 

Is visiting the fish migration a family-friendly activity?

Yes!  If your children are five or older (or younger, if you can carry them) we recommend the 2-mile hiking loop that crosses two bridges, includes nature scavenger hunt cards along the trail, and has a fairy and gnome village. The 2-mile loop can be accessed from the two southern trailheads, see the preserve map for more information.

What are the trail conditions?

The fish can be viewed from our Mill Brook Preserve. These trails follow a beautiful forested valley, so these are hiking trails with steep slopes. Wear solid footwear. Since spring is in full swing, you may want to bring bug spray. 

Photos of Alewife migrating up Mill Brook in both the Northern and Southern viewing pools. Images by Land Trust staff member Brenna Crothers.