River herring population is at its highest since the start of monitoring in the Mystic
Largest of any herring migration in MA
MYSTIC RIVER HERRING RUN 2025: ~ 815,000
Mystic Lakes Dam Herring Count, 2012-2025. The large increase in population in 2015 is the direct result of expanded breeding habitat created by the fish ladder installed in 2012 at Mystic Lakes Dam. Video monitoring data is shown for 2020, when COVID restrictions prevented in-person counts. Short lines on the bars indicate 95% confidence interval, or margin of error.
More than 815,000 river herring passed through the fish ladder at the Mystic Lakes Dam in Medford in 2025 according to the official estimate from the Division of Marine Fisheries (Mass DMF).
815,000 river herring is the highest population estimate since MyRWA volunteers began monitoring at the Mystic Lakes Dam in 2012, and is for the second year in a row - the largest herring migration recorded in the state. In our first year of monitoring, the river herring population was estimated to be approximately 200,000 herring.
"The story of the recovery for River herring in the Mystic River is one of the greatest restoration success stories for Massachusetts in the last 20 years," said Joseph Holbeche, Diadromous Fish Biologist for the Division of Marine Fisheries (DMF). "The success of River Herring in the Mystic is a testament to an amazing partnership between DCR, DMF, MyRWA and especially the amazing volunteers whose stewardship has become invaluable for the recovery of River Herring."
“The construction of fish passages at the Mystic Lakes Dam in 2012 and the Center Falls Dam in 2015 re-connected river herring with more than 200 acres of their ancestral freshwater spawning habitat. Helping herring past these dam barriers and simultaneously improving the health of our freshwater rivers and lakes have created conditions for river herring to thrive in our watershed again,” said MyRWA Executive Director Patrick Herron.
Thanks to community data collection and advocacy, river herring can move freely during their migration from Boston Harbor up to Scalley Dam at Horn Pond. Their population is FOUR TIMES larger today because of these interventions. However, we are not stopping here.
Of the 815,000 river herring that passed the Mystic Lakes Dam, a mere 6,900 were able to make their way up the spillway into Horn Pond. Meanwhile, volunteers observed hundreds more in the pools at the bottom of Scalley Dam, unable to reach spawning habitat in Horn Pond after an over 13-mile journey from the Atlantic Ocean. This missed opportunity for so many herring highlights the need for an improved passage at Scalley Dam.
Many herring make it to the bottom of Scalley Dam and can’t get into Horn Pond. Credit: Keith Ellenbogen
NEXT INTERVENTION PLANNED AT HORN POND
Plans are underway to build a “pool and weir” fish passage — an engineered system of pools along a gentle slope — to get herring past Scalley Dam, the last barrier on their migration route. Herring currently use the rocky Scalley Dam spillway to make their way into Horn Pond. The ability of fish to maneuver through the spillway is highly dependent on water levels and the route requires frequent adjustment of the rocks by Division of Marine Fisheries staff.
Images of the Horn Pond spillway during wet conditions (left) and dry conditions (right). Credit: Weston & Sampson
A fish passage at Scalley Dam will give herring access to 100+ acres of spawning habitat in Horn Pond. With this intervention at Horn Pond, it is estimated that the Mystic River herring run could reach over a million fish (Division of Marine Fisheries). Additionally, viewing areas at this new fish passage, including an underwater window, will allow more people to witness this incredible migration than ever before.
The Horn Pond Fish Passage Project is making progress in the permitting phase and the project team is working to secure the last needed dollars to begin construction. Funding for this new fish passage is coming in part from the Industri-Plex Trustee Council Natural Resource Damages settlement funds and a North American Wetlands Conservation Act (NAWCA) grant.
“The City is eagerly awaiting construction of this important project and the positive impacts it will have on both the river herring and the community. ” said Alex Rozycki, Woburn City Engineer. “We are grateful for the continued funding and support by all involved to provide the enhanced educational opportunities that this state-of-the-art fish passage will bring . We look forward to further supporting the volunteers, monitors, residents and visitors of Woburn by providing accessible access for all to further enjoy Horn Pond”
“As a herring monitor, I see how river herring impact the ecosystem of Horn Pond and support so many other local wildlife. I look forward to seeing the fish passage completed so herring can freely access Horn Pond and so the community can better access and enjoy the migration. Thanks to all involved including volunteer monitors, the Mystic River Watershed Association and the city hall team.” Jeff Dillon President Woburn City Council.
Get involved
In addition to an all-time high herring count, we reached an all-time high of volunteer participation. 225 people volunteered this past spring as weekly and substitute monitors to collect in-person herring counts. Another 89 people volunteered to count herring in videos taken by our underwater fish-cam at the Mystic Lakes Dam to supplement our data coverage of the migration.
About her herring monitoring experience, Lisa Terrazano shared, “I didn't realize when I signed up for this, I would see eagles flying over my head. I live very close to the river in west Medford. I never realized what a valuable resource it is. This was so much fun, thank you for the opportunity and I will be coming back next year.”
The more people that participate and spread the word about this amazing migration that happens each year, the more momentum we can build for getting these important interventions for our watershed.
Here are some ways you can get involved:
Join volunteer opportunities to participate in our in-person and video counting programs. Registration to be a herring monitor for the 2026 season will open in February/March
Spread the word about river herring. Share this video PSA, this storymap about the migration, and gather a group to join our 30th annual Herring Run & Paddle event on May 17th, 2026
Help us improve water quality for all users of the river, people and herring alike:
Donate to our Baseline Water Quality Monitoring Program for Giving Tuesday
Follow Friends of Horn Pond on Facebook to learn about the different species at Horn Pond and how you can help protect local wildlife.
Support the Drought Bill: Drought affects many herring runs statewide. As climate change makes droughts more frequent and severe, we need to be able to strengthen and coordinate our efforts to prevent both our rivers and our communities from running out of water. Check out Mass Rivers Alliance to learn more about the Drought Bill.
Subscribe to our enewsletter for updates about these opportunities and the Horn Pond Fish Passage progress
MORE ABOUT THE IMPORTANCE OF RIVER HERRING
River herring — Alewife and Blueback herring — are migratory species that spend most of their lives in the open ocean, but return to freshwater every year to spawn in the river system they were born in. River herring first return to freshwater to reproduce at 3-5 years old, when they are sexually mature. Fish with this type of life cycle are called diadromous. Diadromous species make up fewer than 1% of all fish species, and they face pressures on their populations in both their saltwater and freshwater habitats. River herring, in particular, are threatened by over-harvesting in the ocean and by the loss of inland habitat for breeding caused by dams blocking access to inland lakes and streams.
Herring have long been an important resource for native people in this area, being used as a food staple, to enrich the soil for crops, and as a signal of the new year. They also have a crucial role in freshwater and marine food webs. River herring are prey for seals, and other marine mammals in the ocean; seabirds, cormorants, ospreys, herons, and eagles; tuna, cod, trout, and several species of bass; mink, fox, raccoon, skunk, weasel and turtles. As zooplankton eaters, they turn an inaccessible resource into the food for a large number of species humans consume, enjoy and profit from.
Today’s commuters on the MBTA Red Line see the name “Alewife” every day, and we at MyRWA celebrate the herring’s return with the annual Herring Run & Paddle race that follows their migration route. Herring continue to inspire movement.
This can never be said enough: all the data we have about the river herring population on the Mystic River we have because of volunteer community scientists. This is public knowledge generated by residents of the watershed. Thank you!!
