An investigation is underway after hundreds of young salmon were found dead at a Coquitlam hatchery, and more dead fish were discovered in the waters of a local creek that feeds into the facility.

Hoy-Scott Watershed Society president Robbin Whachell said residents first spotted dead fish in Hoy Creek on Wednesday and reported it to the city. When Whachell arrived at the hatchery that afternoon, a grim sight awaited her in the tank containing salmon fry.

“Lifted the cover and was aghast what I saw. It was gut-wrenching,” Whachell said.

Piles of dead fish lay on the bottom of the tank. Whachell estimated about 80 per cent of the 5,000 coho salmon that hatchery volunteers had been raising for release next spring had been killed.

“We had people in tears. People saying, 'What can we do?' And you know, a lot of people say 'What can we do?' and the damage has been done,” she said.

Neighbour Maureen Wiebe told CTV News Vancouver she noticed the dead fish in the creek, then found out about the deaths at the hatchery.

“I was just sick. I thought, 'Are you kidding me?'” Wiebe said. “It is so sad. I mean, B.C. is salmon.”

City of Coquitlam environmental projects manager Verne Kucy said water samples have been taken for testing, but the exact cause of the deaths is still unknown.

In a report of the incident, hatchery manager Rodney Lee said city workers who attended the scene suspected a possible release of chlorinated pool water into the creek. Kucy said while not confirmed, it is a possibility. He added chlorine is toxic to fish and is colourless, and there were no changes noted to the creek water.

Whachell said she did notice something different on Wednesday.

"You know when you’re around a chemical, you start tasting something on your tongue. I could smell something. To me, it was similar to when I’m around bleach,” she said.

Until the cause is confirmed, Whachell said there’s also concern for other animals in the area, including wildlife and pets.

“When there’s something that can’t be seen, it’s a bit scary,” she said.

Whachell said hatchery volunteers will now focus on the surviving salmon, but it’s unclear how next May’s planned release may be affected. Every year, the hatchery raises and releases about 5,000 coho salmon fry into Hoy Creek. Just a few weeks ago, on Mother’s Day, they held their annual public release event, where thousands of fish were returned to the water.

“To have this beautiful habitat polluted, and we still don’t know what it is, it’s pretty hard,” Whachell said. “Every storm drain ends up in our waterway. Everything runs downhill, and you have to be cognizant of that.”

The mass death has also been reported to the the Department of Fisheries and Oceans and the province.