Scientists suspect lethal virus behind countless fish washing up dead in Lake Huron

CBC

08-05-2025

Scientists suspect a deadly virus is behind an unusually large number of fish deaths in Lake Huron this spring, where thousands of carcasses have been washing up on Ontario beaches and shorelines from Ipperwash to the Bruce Peninsula.
People living in coastal communities have been posting pictures of the dead fish on social media, showing pale and ghostly carcasses, some of them with bloody lesions, half-buried in sand on beaches, or floating among the debris at marinas and docks along the coast.
While the bulk of the deaths are gizzard shad, a species known for large natural seasonal die-offs, there are also dead rainbow smelt, rainbow trout, yellow perch, log perch, northern pike, longnose gar, largemouth bass and even mudpuppies — a species of salamander that isn't known for die-offs associated with temperature changes in the spring.
Federal authorities said the deaths are likely natural and part of a routine spring die-off, but biologists who study Great Lakes marine life said the sheer volume of dead fish and the breadth of species affected raises the alarm over a possible outbreak of viral hemorrhagic septicemia, or VHS.
'Nasty fish disease'
"[This is] a really nasty fish disease," said Jennifer Powell, a University of Toronto PhD candidate who studies endangered fish on the Ausable River near Grand Bend. "It can wipe out a huge number of fish."
First reported in Lake Ontario in 2005, VHS has since spread to Lake Huron, including Georgian Bay, Lake Erie and Lake Simcoe. While the virus is deadly to fish, it cannot infect humans or other mammals, even if they eat fish infected by the virus.
Powell said concerned citizens have been sending her pictures of dead fish since late April and the reason she suspects VHS is behind the fish die-offs is because many of the images show fish, particularly gizzard shad, that are bleeding on their sides and mouths.
"It's consistent with some of the hemorrhages that can be seen with VHS. These spots don't show up all the time but they can be a sign," Powell said.
"Most of the residents I've spoken to in the Lambton Shores area say they've never seen it this bad," she said. "The sheer volume of it this year is quite unusual."
'Perceived lack of action' by governments
What's also unusual, according to scientists, has been the response to the outbreak from provincial and federal governments, which have yet to confirm whether VHS is responsible for the unusual number of dead fish this spring in coastal communities on Lake Huron.
"I know that VHS is what is known as an internationally reportable disease, that is, if it occurs in your country, you have an obligation to report it to an international agency," said Nick Mandrak, a professor of biology at the University of Toronto who studies fish conservation.
Mandrak, who lives in Grand Bend, Ont., said provincial and federal governments have an obligation, to not only test for and report the disease, but also to inform the public, who are left with little information about the cause of an unusual number of dead fish that have been washing ashore since late April.
"There's quite a few concerned members of the community here," Mandrak said. "They're concerned for, 'is this a human health issue? Can my dog be impacted by this if they were on the beach and played with dead fishes? Is it a water quality issue?' These are questions people are concerned about.
"The perceived lack of action is only magnifying these concerns."
A spokesperson from the Ontario Ministry of Natural Resources and the Canadian Food Inspection Agency could not immediately respond for a request for comment Wednesday.
In an email, a spokesperson from Fisheries and Oceans Canada said it was notified of a fish kill event on Lake Huron near Kincardine on April 26.
"DFO reviewed the available information and at this time we believe the incident is due to natural causes and consistent with other fish kill events that routinely occur during the spring in Ontario."
The Ontario Ministry of Environment Conservation and Parks said in an email Monday to CBC News that it "has not had any reports of spills or observations of smells or water conditions (ie rainbow sheens, unusal cloudiness or colour, etc)."