An estimated 342,000 herring migrated up the Charles River during the spring 2026 season, a 15% increase over 2025, according to new data the Charles River Watershed Association published Sept. 3.
The Charles flows through Needham and Dedham on its way to the ocean, and the annual herring run is one of the clearest measures of the river's ecological health. CRWA said the findings show the Charles supports a significant herring population.
The Massachusetts Division of Marine Fisheries (DMF) analyzed volunteer count data and pegged the 2026 total migration at 342,456 fish, up from an estimated 297,315 in 2025. The margin of error also shrank. It dropped from plus or minus 152,039 last year to plus or minus 44,122 in 2026, a sign the monitoring program is maturing as it enters its third year.
CRWA said that as data collection becomes more consistent, DMF can be more certain of the total migration size.
Volunteer count details
More than 85 volunteers counted herring at the Watertown Dam fish ladder almost daily from April 13 through June 30, 2026. They tallied 41,358 fish, fewer than the 78,674 counted in 2025 but more than the 27,927 recorded in 2024. CRWA said the lower raw count could reflect a delay in the herring run caused by lower temperatures or dam management.
The biggest single day came May 19, 2026, when counters logged more than 12,000 herring. Counters also recorded smaller peaks on May 18 and May 27.
CRWA's Carly Sherman wrote in the report that the organization needs at least two more years of data to compare annual migrations accurately.
Watertown Dam removal funding in play
The data arrives as state lawmakers negotiate an Environmental Bond Bill that includes funding for removal of the Watertown Dam, according to a CRWA legislative update from August 2026. A consultant for the dam's owner, the Massachusetts Department of Conservation & Recreation (DCR), recommended full removal around November 2025, CRWA said.
CRWA has argued that the dam no longer serves a power or flood-control purpose and harms river ecology by blocking fish passage, trapping sediment and depleting oxygen levels. The dam's fish ladder does not work for all species, the association said. Multiple migratory species return to the Charles each spring, including American shad, blueback herring, alewives and striped bass.
At CRWA's third annual Herring Festival on May 17, 2026, hundreds of residents gathered at the dam alongside state Reps. Steve Owens and John Lawn and members of the Wampanoag Nation.
New photo monitoring tool
CRWA also launched a Chronolog photo station at Watertown Dam in 2026. The tool lets community scientists submit photos of the river so researchers can track changes that are hard to spot day to day.
The next volunteer monitoring season begins in April 2027. CRWA has not yet posted registration details for volunteers.
