Massive Fish Kill Causes Thousands of Dead Fish to Pile Up in Massachusetts River

by Jennifer Shea
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Thousands of dead fish have washed up on the shores of the Mystic River, but experts say they died of natural causes and not due to water quality issues.

Along the Mystic River, near Everett and Somerville, Massachusetts, thousands of dead Atlantic Menhaden now litter the shoreline. The fish were still floating in the river as of Thursday afternoon.

Mystic River Watershed Association Executive Director Patrick Herron told CBS Boston that the Atlantic Menhaden probably wound up in the river because they were chased there by a predator. He said he saw a dense school of them, running for hundreds of yards, near the Amelia Earhart Dam last week.

Dead Atlantic Medhaden Pile Up Along Shores of River

Herron said the fish deaths are not a bad omen for water quality. He said it was just nature taking its course that led to their deaths.

“About a week ago, we noticed a large school of Atlantic Menhaden had come into the river,” Herron said. “And that can be a sign of something very positive, a reminder that this river is alive.”

“It can be a little alarming when they come in in such great densities, because as a schooling fish, they can use up all of the oxygen and die,” he added. “And that’s ultimately what happened.”

Authorities are not trying to clean the fish out of the area, but rather are waiting for them to clear out naturally.

“The best thing for us to do is to hold our nose, if you will, wait a little bit and the tides will carry [them] out,” Herron explained.

Kills Occur When Too Many Fish Crowd into a Small Area of Water

Fish kills tend to occur whenever too many fish squeeze into a small volume of water. The same thing happened in the Mystic River in July of 2018, when approximately 50,000 fish died, according to Boston.com.

“When large schools of fish enter warm-water estuaries and rivers in large numbers during the summer months, they can deplete the water’s dissolved oxygen, making survival impossible,” the Massachusetts Division of Marine Fisheries explained in a memo then. “Oxygen must pass across and through fish gills, and when used up by tightly packed fish in shallow waters of narrow embayments, the inevitable occurs.”

As stinky as the Atlantic Menhaden fish kill is for locals, it’s also a good sign, in its own way. For years, there were no Menhaden in the Mystic River due to pollution. Now there are hundreds of thousands.

The only concern now is sewage and fertilizer runoff, which feed algae blooms that draw up oxygen from the water. So if people want to help the Atlantic Menhaden, the best thing they can do is skip the fertilizer.

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