Thornbury dam failure causes fish kill

by Steve Galea | October 4, 2017

Thornbury Dam

A power outage on Friday, September 29 that affected the Town of Blue Mountain for seven to eight hours was also responsible for a major failure at the Thornbury dam on the Beaver River. It caused a malfunction, which opened two of the dam’s three gates, drained the mill pond above the dam, and in turn dried out the fish ladder where fish were stranded and died.

Thornbury Dam

Ministry of Natural Resources and Forestry (MNRF) Senior Media Relations Officer Jolanta Kowalski said, “We estimate there were 60 to 70 fish killed that were mostly salmon and 90% male.”

Kowalski said alarms made MNRF staff aware of the issue. She said a response team was on site early Saturday morning and closed the dam manually. Eventually, the mill pond rose to its normal level and returned water to the fishway by late afternoon.

John Kendell, president of the Credit River Anglers Association, was visiting the river from Oakville and was preparing to fish Beaver River at 6:15 a.m. that morning when he noticed the issue.

“I was shocked and horrified to see that the ladder and dam had failed in the night,” he said.

Kendell said he counted around 100 stranded and dying fish, he estimates 70 of them were salmon and 30 were steelhead. The fish ranged from five to 15 pounds in size. He also saw smaller fish such as young rainbow trout and minnows, too.

Thornbury Dam

“My bigger concern was the huge amount of water, silt and mud in the river,” he said. “There was mud on rocks two feet above the regular water levels.”

Kendell said he called the MNRF hotline at about 6:30 a.m. and left a message. He then contacted friends who knew how to get hold of local MNRF staff to alert them of the issue.

By 10:30 a.m., he said MNRF staff were on site.

He and other local anglers helped MNRF staff collect the dead fish and clean up the site.

The dam, owned by the MNRF, is once again operating normally. Kowalski said MNRF staff is still assessing what caused the malfunction to the dam and fishway, which underwent major construction in 2003.

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