A Fish Die-Off in High Park's Grenadier Pond Perplexes Officials
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A Fish Die-Off in High Park’s Grenadier Pond Perplexes Officials

Officials don't know why hundreds of fish died in High Park's Grenadier Pond earlier this week.

Dead fish in Grenadier Pond on Wednesday.

The stench was noticeable within twenty metres of the shoreline. Earlier this week, there were hundreds of dead fish in groupings of dozens along the southeast side of High Park’s Grenadier Pond, some floating, some half-eaten, others bloated with decomposition. The die-off happened days ago, but officials still aren’t sure what caused it.

“I found out about it on Monday morning,” explained Lenka Holubec, a volunteer with the High Park’s natural environment committee. “I come down here to check on the pond, and I walk the trail usually twice a day, because of the lines that some fishermen leave behind.”

“As I walked, I noticed that after the pier there were dead fish,” she said. “It wasn’t until I saw all these juvenile fish, of various species, in layers lying on the shoreline, being eaten by the birds around, that I became horrified by the sight.”

“I was just walking and breathing,” she explained. “[My reaction] was delayed because at first it was a few dead fish, but then it was a lot of dead fish, and the smell was so intense that day because it was sunny and hot. It was extremely strong.”

Rick Portiss, the supervisor for environmental monitoring at the Toronto and Region Conservation Authority, also found out about the occurrence on Monday.

“It was passed on to my boss,” he said. “He came to me saying that we should go down to Grenadier Pond because there’s been a fish kill.”

“It looks like species that use the shallow water areas are the ones affected,” Portiss said. “We just went for a little tour to look around Monday and saw the pan fish lying along the eastern shoreline.”

Among the dead fish were the usual “pan fish,” such as pumpkinseed fish. There were some small bass, rock bass, perch, and a juvenile pike. “We haven’t seen a fish kill of this size in a while,” Portiss said.


TRCA’s team used a HydroLab—a piece of portable testing equipment—to take measurements of the water’s temperature and amount of dissolved oxygen. They suspected that a lack of oxygen in the water, possibly caused by an algal bloom or water stagnation in hot weather, was the culprit. This turned out not to be the case. “Everything seemed to be fine and we’ve ruled out anoxia,” Portiss said. “The next step is a chemistry test by the MoE [Ontario’s Ministry of the Environment] and MNR [the Ministry of Natural Resources]. We’ve handed over the investigation, because we’ve gotten as far as we can.”

“What we know at this point is that various species were killed in Grenadier pond,” explained Jolanta Kowalski, a spokesperson for the Ministry of Natural Resources. “So we are sending water and fish samples to the University of Guelph for analysis.”

However, according to Kowalski, the analysis will take time.

“Water samples can take a couple of weeks,” she said. “Depending on how busy the lab is. But the fish samples, I’m not sure how long it could take.”

According to Kowalski, the ministry has encountered situations similar to this before, although there are usually stand-out circumstances, like a recent storm or extreme temperatures. This time is different because of the variety of species affected. Ministry officials don’t have any specific concerns about contaminants, and haven’t said the pond water poses a risk to public health.

Even so, Kowalski recommends that locals keep their pets away from fish carcasses, “as we would normally tell the public not to let their dogs eat dead and decaying things.”

Park patrons can breathe easy, and deeply, because the City will be taking on the cleanup project, according to the acting supervisor of High Park, Dave Chapman.

“We don’t get our feet wet,” said Chapman, referring to the water in the pond, which falls under the Toronto and Region Conservation Authority’s jurisdiction. “But we are going out and guiding some of the long-handled pool skimmers to clean up the fish as they get close enough to the shore that we can reach them. We’re just waiting for them to come into shore, but as they come in, we will be cleaning them up.”

Photos by Giordano Ciampini/Torontoist