Dead fish removed by city crews from Waterloo pond after die-off

Dead fish found floating in a stormwater retention pond in Waterloo have been cleaned up by city workers.

The pond is located in the residential area of Erbsville Road and Creekside Drive.

It's unclear how the fish died, but Jessica Kellerman, the city's manager of stormwater operations and construction in city utilities, said it's not believed that anything was dumped in the pond to kill the fish.

"It is fairly common after really harsh winters to see in shallow lakes, in some creeks, in stormwater ponds, something called winter kills," Kellerman said. "Basically it's where the freeze-thaw cycle is so extreme during the winter that you do end up getting because of the conditions, What can happen is the ice freezes over so thick that it sort of starves the water of oxygen."

Kellerman says city crews didn't report anything amiss at the pond that would suggest contamination such as an unusual odour, a shine on the surface of the water or anything in the dirt along the banks of the pond.

"We do regular checks of our stormwater ponds and we also will go out and do maintenance as needed. So a lot of people have had eyes on these facilities. We know what to look for. We know if something doesn't look right, if it's strange," she said.

Not a good environment for fish: Expert

Jim McGeer is a biology professor at Wilfrid Laurier University in Waterloo and co-director of the Laurier Institute for Water Science.

He noted stormwater management ponds are not made for wildlife because the ponds are meant to filter water before it makes it to rivers and groundwater sources.

"You wouldn't necessarily expect to find a lot of fish there. It's not an environment that is really very conducive to fish and life," he said, adding the water in the ponds flows in from nearby subdivisions.

"It's coming from all the stuff that washes off of local neighbourhoods and it all ends up in the pond and hopefully it's trapping some of those contaminants before they get released. That's what they're supposed to do."

Kevin Stevens who is an associate professor of biology at Laurier and also co-director of the Laurier Institute for Water Science, said they've been testing stormwater management ponds in Waterloo region to understand how the ponds were performing.

"In particular, we were interested in what was happening in the winter because they're not normally looked at in the winter. So we were trying to find out what the quality of water was that was coming into the ponds at different parts of the season, different parts of the year, and to see how well the ponds were doing in cleaning up some of those contaminants," he said.

Stormwater ponds considered infrastructure

Stormwater management ponds don't tend to have plant life. In a regular pond setting, plants would create oxygen and can keep fish alive when the surface freezes over. Without plants, when the pond freezes over, there's no chance for oxygen to go into the water from the atmosphere.

"There was a very prolonged period this year with ice cover that would have impacted the oxygen levels," Stevens said.

As for how the fish got into the pond in the first place, that's another mystery, McGeer said. It could have been people dumping unwanted fish in the pond or birds may have inadvertently dropped live fish or a fish carcass with eggs inside it into the pond, allowing those eggs to hatch in the pond.

The pond in Waterloo is considered an "offline" facility, Kellerman says, meaning it has no direct connection to the creek system. Water is meant to sit in the pond to allow contaminants to be filtered out.

Kellerman says while it can be distressing for people to see this kind of die-off, it's also important for them to remember the ponds are not meant to be habitats.

"Water management facilities are pieces of infrastructure, they're not built for habitat," she said.