MYSTIC RIVER HERRING RUN 2024: ~640,000
More than 640,000 river herring passed through the fish ladder at the Mystic Lakes Dam in Medford in 2024 and around 37,500 herring made it into Horn Pond according to the official estimate from the Division of Marine Fisheries (Mass DMF).
This year’s total at Mystic Lakes was higher than any in the past five years, representing the highest population in the Mystic River watershed since 2019 and the largest river herring run in all of Massachusetts this year. River herring is a species of fish that lives in the ocean and returns to fresh water to spawn (lay their eggs). They are loyal to the lakes, ponds and rivers where they were hatched, and are an important part of the oceanic and riverine food web.
A volunteer monitor counting herring as they exit the Mystic Lakes Dam fish ladder. Credit: David Mussina
“That the most urbanized watershed in New England is also home to the largest river herring migration in the state is nothing short of remarkable,” said Daria Clark, MyRWA Senior Engagement Manager. “Our detailed knowledge of this major wildlife migration exists only because of the commitment of hundreds of community science volunteers who collect the data, and the migration itself is a testament to a concerted effort by residents, MyRWA, and agencies to create fish passages and improve water quality.”
The Mystic River herring population is poised only to grow after fish get better access to the next large freshwater body in the system — Horn Pond. Planning is underway for enhanced fish passage at Horn Pond, with the project currently in the permitting phase.
The official estimate for our herring run population comes directly from the 10-minute counts these volunteer monitors obtain every daylight hour, 7 days a week, from April through June.
Figure 1. Mystic Lakes Dam Herring Count, 2012-2024. 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.
Figure 2. Horn Pond Herring Count, 2018-2024. Short lines on the bars indicate 95% confidence interval, or margin of error. This year, three times the number of herring were able to enter Horn Pond compared to 2023. Herring currently use the rocky Scalley Dam spillway to make their way into Horn Pond.
THIS YEAR’S INCREASE IN POPULATION
This year’s count represents the latest chapter in the major ecological restoration story of river herring in the Mystic. Since 2012, the Mystic herring population has more than doubled, due to the construction of fish passages at the Mystic Lakes Dam and the Center Falls Dam, which introduced more than 200 acres of freshwater habitat for herring to spawn.
In the years since these major improvements, the Mystic river herring run has remained relatively stable. According to the Division of Marine Fisheries, the recent increase in 2024 likely is the result of the big migration year of 2019. Herring born during 2019 are now reaching mature spawning age and are returning to the river. Additionally, plentiful rain early in the season aided the herring’s migration, especially at Horn Pond.
IMPROVEMENTS COMING TO HORN POND
An overhead view of Scalley Dam at Horn Pond with the rocky spillway on the left. Credit: Tyler Hilliard
We are encouraged to see three times the number of herring able to enter Horn Pond this year compared to 2023. Herring currently use the rocky Scalley Dam spillway to make their way into Horn Pond. Each year, the Division of Marine Fisheries team maneuvers the rocks the best they can to allow for pools herring can use to travel up into the pond. However, the accessibility of this route is highly dependent on water flow and can be severely restricted during periods of drought. This year, early spring rains made it relatively easier for fish to navigate the channel.
But herring monitors still observed hundreds of river herring in the pools at the bottom of Scalley Dam, unable to pass this last obstacle to breeding habitat in Horn Pond. We know that many more river herring would take advantage of the high quality breeding habitat at Horn Pond if they could freely enter the lake.
Plans are underway to build a “pool and weir” fish passage — an engineered system of pools along a gentle slope — that will give many more fish access to the pond. The Horn Pond Fish Passage project is currently in the permitting phase. Funding for this new fish passage is coming in part from the Industri-plex Damaged Natural Resources Council in conjunction with the February 2020 Restoration and Environmental Assessment Plan.
Upon the completion of this project, herring in the Mystic River watershed will have access to much of their ancestral range. With an easier, more consistently available route to reach 100+ acres of spawning habitat in Horn Pond, it is estimated that the Mystic River herring run could reach over a million fish. Additionally, viewing areas at this new fish passage, including an underwater window, will allow more people to witness this incredible migration than ever before.
“These improvements will make it so wildlife and people alike can better enjoy the spectacular natural resource that is Horn Pond,” said Jay Corey, Woburn City Engineer. “We are grateful for the new educational opportunities this fish passage will bring to the community and to all the herring monitors that have volunteered their time to help the herring migration.”
“I am thrilled to see so many herring make their way to our crown jewel Horn Pond. As a herring monitor, I see the positive impact more herring has on local wildlife. I look forward to even more exciting times when the fish passage is fully funded and completed. Thanks to all involved including volunteer monitors, the Mystic River Watershed Association and the city hall team.” Jeff Dillon President Woburn City Council.
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 for food, as fertilizer 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.
GET INVOLVED
Will the Mystic herring run reach a million fish? Will the Mystic continue to lead the state in herring populations? Stay tuned for more data from a remarkable urban wildlife migration.
In the meantime, keep an eye out for volunteer opportunities to participate in our in-person and video counting programs. Registration to be a herring monitor for the 2025 season will open in February/March. Plus save the date for the Herring Run and Paddle on May 18th, 2025. Subscribe to our enewsletter to be notified when registration opens for these opportunities.
And finally, 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!!