Why Are So Many Dead Fish In The Gowanus Canal?

GOWANUS, BROOKLYN — Add "heaps of dead fish" to the concerns swirling around the polluted Gowanus Canal.

Woke up to a bunch a dead fish in the Gowanus Canal in Brooklyn. Pray for the little fishes and crabs holding on for life around them. The fact this is now a superfund site, building a city around a canal doesn’t seem fishy at all. pic.twitter.com/wJevunFdP3
— janellaboo (@xavichopchop) July 15, 2023

But the mass death recorded in vivid, putrefying detail over the weekend by concerned locals is unlikely to be of lasting harm to the canal's growing schools of fish, said Gary Francis, the captain of the Gowanus Dredgers stewardship organization.

A combination of factors, including combined sewage overflow into the canal from recent heavy rain, caused oxygen levels to plummet and suffocate juvenile Atlantic menhaden, commonly known as bunker, Francis said.

"I know that looked like a huge amount of fish, but there are so many more fish in the canal," he said.

The juvenile, or "peanut," bunker are among many species of fish that have rebounded in recent years as the Gowanus Canal has been cleaned.

And die offs of peanut bunker and over fish aren't unheard of in the canal, or other waterways within New York City, as recounted in a 2020 Gothamist report.

What happened over the weekend was outlined in broad strokes by Francis in a video posted Sunday by the Gowanus Dredgers and in more detail with Patch.

Francis stressed he's not a scientist, but recounted experts' thinking. He said ongoing "capping" meant to contain contaminated sediment in the canal has led to suspended particulates in the water.

To help those suspended particulates settle on the canal's bottom, engineers have turned off the Flushing Tunnel, which normally pumps oxygenated water into the waterway like a giant aquarium aerator, Francis said.

"Then you have a rain event that can shock the whole system very quickly," he said.

The "shock" in question included combined sewer outflows into the warm, temporarily very still and already oxygen-poor water, Francis said.

The plummeting oxygen levels killed off the weaker peanut bunker, he said.

But Francis, although upset about the die off, stressed that the fish will recover.

"I know the bunker will be back in, probably within days," he said.

Any mass fish death in the Gowanus Canal perhaps understandably elicits fear, given that it is an EPA Superfund Site because of its decades of industrial pollution.

But as Francis pointed out, the fact that peanut bunker and other fish are in the water in such numbers is a sign the canal is recovering.

"It gives me hope that if we can save this horribly maligned water body, then we can save the planet," he said.

And, in the meantime, the circle of life carries on within the canal. The dead fish have been a short-term boon for wildlife such as shorebirds that got an unexpected feast.

"The blue crabs are loving it," Francis said.