It's not an oil spill, just clumps of dead fish flies floating in the Detroit River

The reddish brown clumps being carried by the current are actually dead piles of fish flies. That might make you cringe, but it's actually a good sign.

Fish flies are a sign the river is getting healthier

Dead fish flies floating along the Detroit River, July 5, 2019. (Chris Ensing/CBC)

From a distance, it may look like there's been an oil spill in the Detroit River this time of year. But it's nowhere near as serious — it's just smelly.

The reddish brown clumps carried by the current are actually dead piles of fish flies. That might make you cringe, but it's actually a good sign.

Piles of dead fish flies float down the Detroit River and officials say it's actually a good sign. 1:45

"As much as they smell and get around your house, they're actually a sign that the river is getting healthier," said Peter Berry, harbour master with the Windsor Port Authority. "It's a good sign that the river has the oxygen for it, that the plants are providing the place for it to start out its life."

After that, the mayflies die in just a few days. On the bright side they're still beneficial after death, becoming food for birds and fish.

"It looks like an oil spill at first glance, so we do get calls saying there's something in the river," said Berry.

And Berry has noticed an steady increase in the amount of fish flies over the last 10 years. This year, he says, they're breeding a bit later.

"The high water, of course, has eroded many shorelines, the habitats of lots of species as well," said Berry. "Typically we're seeing them earlier in the month of June.

Peter Berry, harbour master with the Windsor Port Authority, said he gets calls about the dead fish flies from people thinking it's an oil spill. (Jason Viau/CBC)

Nasty side to fish flies

Berry said he couldn't think of any negative aspects of fish flies. Oh, except for the people who live near the water and have swarms descend on their neighbourhoods.

"There's no worse feeling than having the smell of fish in the driveway in the morning and that crunch beneath your feet," said Berry.

Get your nose plugs out, he expects fish fly season to last another few weeks.

Click below to watch a video of someone in our region powerwashing fish flies off his driveway in Windsor-Essex in 2017: 

About the Author

Jason Viau is a video journalist, TV host and radio newsreader at CBC Windsor. He was born in North Bay, but has lived in Windsor for most of his life. Since graduating from St. Clair College, he's worked in print, TV and radio. Email him at


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