Dead Fish Surface at Vermilion Lakes, Area Partially Closed

In recent weeks dead fish have surfaced beneath the ice at Vermilion Lakes in Banff National Park, prompting Parks Canada to issue a spot closure in parts of the area.

Parks Canada says the fish die-off is caused by “winterkill,” a natural event that happens when oxygen levels in the water drop too low. This often occurs during winters with thick ice and heavy snow. The ice and snow block sunlight from reaching the water, which limits plant growth. Without enough sunlight, aquatic plants stop producing oxygen and instead begin using it up as they break down. “This results in a decreased amount of oxygen available to aquatic life below the ice, which can cause mass die-offs in fish,” said Tomi Postma, public relations and communications officer for Banff National Park.

Winterkill has occurred at Vermilion Lakes in the past and primarily affects suckers, a species native to Bow Valley waters. Although the abundance of fish carcasses may appear visually concerning, sucker populations in the area remain steady. The species’ high reproductive rate, with individual fish capable of producing between 20,000 and 100,000 eggs depending on size, contributes to their ability to repopulate following die-off events.

Vermilion Lakes may be especially prone to winterkill because they are relatively shallow. In shallow lakes and ponds, there is simply less water to hold oxygen during long periods of ice cover, which makes it easier for oxygen levels to drop to dangerous levels for fish.

Records show winterkill at Vermilion Lakes as far back as 1959. While similar events may have happened over the years without being formally recorded, large fish die-offs were clearly documented in 2023, 2024 and again this winter in 2026.

Local fishing guide Brad Murphy said he has seen similar events in the area before.

“We do see it from time to time on the river with suckers of that size,” said Murphy, owner of Canmore Fishing Adventures.

Although not an abnormal event, Murphy raised questions about its possible link to fish movement in the area, noting that rail lines appear to separate parts of the lake system from the Bow River, potentially making it difficult for fish to leave before freeze-up.

“Essentially cutting the fish off from the river and making it difficult for them to navigate out of the lake during the winter months,” said Murphy.

To support his claim, Murphy pointed to Lac des Arcs east of Canmore as an example where a constructed dike and the seasonal closure of culverts, which are drainage pipes that allow water to flow under roads or rail lines, can affect fish movement.

“The dike that forms Lac des Arcs was built to keep water in the lake to prevent dust entering the hamlet in the winter. Connected by culverts that get closed in the fall/winter. Here again the fish can find their way in during the spring and summer months, but have difficulty finding their way out before getting trapped during low water in the fall then under the ice in the winter,” said Murphy.

Additionally, Murphy raised concerns that the frequency of winterkill could increase as Alberta experiences declining river levels during the summer due to lower-than-normal winter snowpack in the Rockies, rapidly melting glaciers and earlier spring runoff. These conditions can cause the connecting waterways that feed back into the river to dry up earlier every year.

“As we continue to see declining river levels by late summer, the possibilities of these fish getting trapped more frequently will definitely increase as connecting waterways that lead back to the river lose their water earlier every year,” said Murphy.

Parks Canada has not confirmed a connection between winterkill and fish mobility or water levels in the area. However, the agency has implemented public safety measures, including a site closure with no set end date, amid concerns that decaying fish could attract predators such as bears.

“Winterkills can result in many fish carcasses, which are wildlife attractants, and draw in scavengers and predators,” said Postma.

To prevent human-wildlife encounters, Parks Canada has issued a spot closure similar to the one implemented during the winterkill event in March 2024 in the same area.

“A spot closure has been issued for the Vermilion Lakes area until further notice. The goal of the closure is to minimize disturbance to wildlife so they can feed on the abundant food source,” said Postma.

The closure does not affect access to Vermilion Lakes Drive, nearby trails or most areas where visitors access the frozen lake. Signage has been posted on site, and Postma encouraged visitors to respect the closure to ensure the safety of both people and wildlife.

“Parks Canada implements area closures and restrictions to protect ecologically sensitive areas, important habitats for sensitive species or species at risk, and locations where the potential for conflict between humans and wildlife is high. Please respect all area closures,” said Postma.