The rocks along Water Street in Brunswick, Maine went silver over one weekend this fall.
Small river herring lay scattered along the shore.
A local advocate walked the bank and counted.
He did not need a lab or a drone to get a number.
He needed a measured stretch of shoreline and a strong stomach.
The number he got is still the only one anyone has published.
How a four hour window ended up on the riverbank
The mechanism here is almost embarrassingly simple. A single hydroelectric turbine at the dam between Brunswick and Topsham had been idled overnight as a precaution, because the dam’s owner had been told that crews were going to lower Sabattus Lake for the season. Drawing a lake down pushes young river herring out all at once, sending a concentrated pulse of fish downriver together instead of a trickle.
The point of the shutdown was to let that pulse past the plant rather than through the machinery. The company says it initiated a nighttime shutdown to allow safe passage for alewives heading for the Gulf of Maine, but that a single turbine went back on for four hours on the Saturday.
The result showed up on the rocks that weekend. That is the whole mechanism: a four hour overlap between a turbine spinning and a lake being drawn down upstream. No storm, no broken part, just a window of running machinery lining up with a window of fish.
What the riverbank actually looked like that weekend
Walk the bank in Brunswick and the scene is specific. Dead river herring littered the shore after the weekend mortality event, with many of them visible along Water Street. They were young fish, the season’s crop, headed downstream toward the sea.
The advocate who publicized it, Chip Spies, founded a local group called Free the Andro.
The group has been advocating for better fish passage at the dam during its federal relicensing period, and reported herring “lining the shores” along the river. A second local nonprofit, Friends of Merrymeeting Bay, supplied photographs of the fish.
The operator did not dispute that a kill happened. A spokesperson for Brookfield Renewable said the company was aware of the weekend’s fish mortality event and that the dam had been offline since Saturday to prevent further deaths. You can read the original local reporting on how the scene was found.
The one real count, and the number nobody has
Here is where the story gets precise. Rather than estimating across the whole river, Spies counted fish along a short run of shoreline he could actually walk.
“I counted about 30 fish per yard, so that’s 3,000 fish right there in this little stretch,” he told WGME. That is the floor, not the total.
The other number on the table came from the company, which said that after personnel observed fish mortality downstream on Saturday morning they shut down generation completely, and it remained offline “to support the estimated 1 million migrating herring.”
So the two hard figures are a counted 3,000 fish along one stretch of bank and an estimated million herring in the run overall. Nobody has published a river wide mortality figure. The word “thousands” in the headlines rests on that single measured stretch.
Why a four hour gap is bigger than it sounds
A turbine blade does not have to touch a fish to kill it. Rapid pressure change causes physical damage to body tissue, and commonly observed barotrauma injuries in fish include swim bladder rupture, hemorrhaging and gas embolism. A fish can look untouched on the outside and already be finished.
Federal laboratory crews have mapped those conditions with an autonomous sensor package that records multi axis acceleration as it passes through the turbine environment, showing where live fish may be striking structures. Rapid pressure change is only one of several hazards during turbine passage, alongside blade strike, shear and turbulence.
None of that requires a cracked part or a bent gate. It only requires the wrong machine running during the wrong few hours. Researchers have found that keeping minimum pressures higher near the turbine is central to any machine that is truly “fish friendly.”
What happens now that the plant has gone dark
The operator kept the facility offline afterward, choosing zero output over running machinery into another wave of herring. The project has three turbine generators with a combined installed capacity of 19 megawatts, so that is a real cost to absorb voluntarily, and it bought time for the rest of the run to pass.
The dam sits at the head of tide, the first barrier migratory fish face on the Androscoggin as they try to reach their spawning grounds, which is why a few hours of operation can land on so many fish at once. None of this settles the dam’s future, which sits inside a federal relicensing process that will not conclude soon.
But it leaves a cleaner lesson. The only measurement from that weekend was a counted 3,000 fish in one stretch of bank, small enough to tally by hand and large enough to shut a plant down, a reminder that the balance built into energy infrastructure is never settled, whether the structure is a dam, a steel platform in a Massachusetts canal or farmland shared with solar panels.
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