Born to Run: Reflections from Alewife Migration Season

Clara Franzoni, a Regional Land Trust Fellow, reflects on her Spring season witnessing the annual alewife migration while working at her host site, the Presumpscot Regional Land Trust. She shares the history of the remarkable partnerships and advocacy efforts that have allowed this migration to return, allowing her to promote the importance of river and land conservation today.

When I began my fellowship position in January with the Presumpscot Regional Land Trust (PRLT), alewife migrations were a distant concept. Each spring in mid-May, thousands of fish swim upstream through Mill Brook on their way to spawn. These fish swim right through PRLT’s Mill Brook Preserve, allowing an opportunity for visitors to witness a natural migration up close that many in the area are unaware is even occurring. PRLT’s staff were so enthusiastic about the fish’s return as a sign of spring and repeatedly told me how incredible it was to witness each spring, so much so that it landed them on the cover of National Geographic. 

Hiking Mill Brook Preserve in February to see a very frozen viewing pool

In the peak of January’s winter snowstorms, the thought of thousands of fish returning into the rivers that were now frozen and covered in inches of snow was difficult to wrap my head around. I spent my winter diving into research, preparing myself for fieldwork, and gathering information for walks that would revolve around these fish. Through my research and conversations with partners, I was shocked to learn about the history of the migration and how it disappeared for over 250 years.

What it looked like at peak migration in late May with hundreds of fish! 

Alewife, a species of river herring, is a type of anadromous fish. This means that they hatch in freshwater, migrate to saltwater to feed, grow, and mature before returning to freshwater to spawn. Alewives range from Florida to Newfoundland, making migrations each spring from the continental shelf into freshwater lakes to spawn. These fish are natal spawners as well, meaning they return to the same lake where they hatched and were raised as fry, or juveniles, to spawn themselves as adults. The local alewife population migrates 11 miles from Casco Bay, up the Presumpscot River, and into its tributary of Mill Brook before spawning at Highland Lake.

The history of the Presumpscot River’s usage and water quality is a complicated one, where industrialization and urbanization within the watershed began to cause blockages in the river that would hinder fish migrations. Historically, about 10 migratory fish species moved through this watershed, many like the Alewife, which would travel to Sebago Lake to spawn, which is more than 24 miles away. Yet, over time, dams, culverts, and general development blocked these routes, and those migrations largely disappeared. 

On the 250th anniversary of America’s Declaration of Independence, the concept of a fish migration disappearing for almost the same amount of time is hard to conceptualize. At Presumpscot 2040, a partnership project revolving around the future of Presumpscot River led by Casco Bay Estuary Partnership and partners like PRLT, Friends of the Presumpscot River, Friends of Casco Bay, Maine Department of Environmental Protection, Sebago Clean Waters, the Town of Windham, and Trout Unlimited, I learned more from locals who grew up on the Presumpscot River and have witnessed its development and other risks to river health. At the event, Michael Shaughnessy at Friends of Presumpscot River spoke about the river’s history and highlighted Wabanki Chief Polin, who, in 1739, walked to Boston to meet with Governor Jonathan Belcher, protesting the recent dams built along the Presumpscot River, which he called “the river to which I belong”. The Wabanki valued migratory fish like Alewife, calling them “siqonomeq” or “the fish that feeds all.” Early colonial dams within the Presumpscot River watershed blocked these migrations, and Chief Polin requested of the Governor “only that a place may be left open in the dams so that the fish may come up in the proper seasons of the year.” These requests were largely ignored over time as more dams and mills were built along the watershed, and wastes from mills and sewage were dumped into the River. By the 1930s, the Presumpscot River was categorized as one of the most dammed rivers in the country. 

In recent decades, a series of efforts have helped to allow for the alewife migration to successfully travel through the Presumpscot River, including the removal of Smelt Hill Dam in 2022 (now around 8 dams remain along the Presumpscot River), replacement of culverts, and installation of a fish ladder at Highland Lake. Since Highland Lake was not the historical spawning location of the alewife, a spawning population of alewife headed to Androsoggin Lake were introduced to Highland Lake in hopes of a successful natal spawning return from the fry, around 4 years later, when they reached maturity. Over time after the Smelt Hill Dam was removed in 2002, fish have been able to travel through Mill Brook and return to Highland Lake to spawn. 

PRLT conserved what is now Mill Brook Preserve in 2016. At 130 acres, it is the largest conserved land in Westbrook and was able to be protected through partnerships like the City of Westbrook, landowners, and the Casco Bay Estuary Partnership. Conserving the riparian ecosystems surrounding Mill Brook allows PRLT to protect this tributary of the Presumpscot River for the alewife migration, since Mill Brook now functions as the natal spawning Alewife population’s sole migration corridor and access route to spawning habitat. 

PRLT staff and volunteers established two Viewing Pools in Mill Brook Preserve at natural falls and eddies where the fish pool and rest during their migration, to allow visitors to view the migration from different stages. To help people get the most out of their visit to the Southern Viewing Pool in Mill Brook Preserve, PRLT works with the Gulf of Maine Research Institute each year to produce a digital guide to the migration. This year, I also received training from their scientists in the Fisheries Ecology Lab on the science and ecology of migration. 

This enabled me to lead more guided walks through the Mill Brook Preserve. More walks meant more people in the surrounding community who were able to access and learn about this natural wonder that was happening in our backyard. 

Filming with Evergreen Credit Union, partner of PRLT and adopt-a-trail sponsor for Mill Brook Preserve, on an informational video about the migration

I led private educational walks with local schools like Windham Middle School and homeschooled students, joint walks with GMRI staff, walks with partners like Westbrook Public Services and Sebago Clean Waters, and four public walks spanning the start and end of the migration season from mid-May to the first week of June. Within these walks, I had the opportunity to talk about the significance of alewives to our ecosystem and the challenges they face during their spawning run, including the significance of the Presumpscot River and Mill Brook for migrating fish and the importance of river stewardship and conservation work like PRLT and its partners uphold. 

Leading a public Alewife Migration Walk for PRLT with more than 30 attendees!

World Fish Migration Day was May 23, 2026, which aligned perfectly with the start of the migration season within the Presumpscot River and Mill Brook. PRLT joined partners Friends of the Presumpscot River, Trout Unlimited, Discover Downtown Westbrook, and Portland Trails for a celebration in downtown Westbrook, talking about the history of river restoration and dam removal within the Presumpscot and the successful migrations for fish like alewife. 

Every year, PRLT also organizes the volunteer fish count at the Highland Lake dam, where the alewives use the fish ladder to leave the river and enter the lake’s channel to spawn. I oversaw over 30 volunteers who signed up for shifts to monitor the number of fish entering the lake during a 30-minute timeslot, and we use these counts to estimate daily and annual totals of the successful run. The data goes to University of Southern Maine, Maine Department of Marine Resources, and partnerships like Manoment Conservation Sciences and their Gulf of Maine River Herring Network.  

The fish ladder! At its peak, thousands of fish a day swam up this ladder and into Highland Lake

It was here at the dam, when I was training volunteers on how to monitor the fish ladder, that I saw my first fish use a fish ladder and enter a dam. I nearly jumped into the air at the sight of these fish! A fish I had researched for months was successfully making the migration they were meant to, with the timing aligning with historical expectations. In the next two weeks, I would receive daily calls and emails from dedicated volunteers, sharing this joy at the sight of thousands of fish entering the dam through the fish ladder. As I input the data and extrapolated it to predict the total population of fish that entered the dam, I was able to witness daily changes due to rain and water levels and other natural barriers seeing how the migration slowed and picked up. This year’s estimated numbers were huge: over 63,000! This has grown considerably since 2021 the first year PRLT took over the initiative from USM, when we only had counted around 40,000 estimated fish. 

Despite the spawning run only lasting around two weeks, there were months of partnership preparations, data updates, collaborations, and network support before and after the migration season. This migration is relatively small compared to others in the state, but as I learned, this region’s support and advocacy for river restoration, protections, and monitoring has led to a large network of support through non-profits, research institutions, and state and town facilities. As my service with PRLT transitions away from alewife outreach and monitoring toward conservation work like water quality monitoring, I am reminded again by how interconnected this conservation work is within the Greater Portland Region and the Presumpscot River watershed. 

PRLT has worked for nearly a decade to monitor, preserve, and enhance the health of the Presumpscot River and its tributaries for the benefit of recreation, public health, and ecosystem biodiversity. We participate in the Maine Department of Environmental Protection’s (DEP) Volunteer River Monitoring Program (VRMP), sending dedicated volunteer water stewards throughout the Presumpscot watershed every other week from May through September. Volunteers test river water for dissolved oxygen, water temperature, and conductivity, as well as collect water samples to be tested for E. coli bacteria. With donor support from Casco Bay Estuary Partnership and advisors at Friends of Casco Bay and Maine Department of Environmental Protection, I am supporting PRLT to expand the water quality monitoring program to observe daily changes in water quality parameters with continuous water quality sensors. 

It was during this Spring season with PRLT that I was really able to witness how clean water and healthy, productive river ecosystems require keystone species like alewife, along with restoration and conservation efforts that protect riparian ecosystems, river passages, and maintain clean water. I am grateful to be serving with PRLT through GPCOG’s Resilience Corps fellowship. This opportunity has provided me with the opportunity to engage in public outreach, species and data monitoring, and conservation work alongside incredible partners in the region. The fry hatching at Highland Lake will begin their journey downstream into Casco Bay and the Gulf of Maine at the end of summer. As we continue our research and the seasons transition, I will always remember the Spring I spent with the alewives!

About Clara

Clara grew up in Clinton, Connecticut, where she first fell in love with spending time on the water and outdoors. She recently earned a bachelor's degree from the University of New Hampshire in both Environmental Conservation and Sustainability and International Affairs. Throughout her college career, she engaged in environmental public outreach and naturalist roles with Connecticut State Parks and a fellowship with New Hampshire Sea Grant, as well as worked as an undergraduate research assistant at UNH's Coastal Restoration and Resiliency Lab. She also studied abroad in New Zealand, conducting field research on benthic invertebrates in local wetlands affected by flooding. As a Resilience Corps Fellow, Clara is excited to work with the Presumpscot Regional Land Trust on stewardship, land acquisition, and outreach. She looks forward to exploring the Portland region and connecting with passionate locals through the Resilience Corps fellowship. In her spare time, Clara enjoys spending time outside and on the water, reading, thrifting, listening to live music, and taking pictures.