Zombie Fish Multiply Rapidly in Lake Superior’s Deep Waters

A study of the gray trout populations in Lake Superior, North America, has revealed a worrying trend over the past decade: salmonids that are abnormally emaciated, nicknamed “zombies.”

Not Quite Spry Fish

Belonging to the salmon family, the gray trout, or siscowets, are known for dwelling in the deepest layers of Lake Superior. While these fish typically present a fairly stout silhouette, thanks to substantial fat reserves that help them endure the icy temperatures of the region, an increasing number of individuals exhibit body fat three times lower than normal.

In 2015, about 3% of the gray trout caught were considered “zombies.” Ten years later, more than 50% of the specimens fished at Superior Maximus, the deepest point of the world’s largest freshwater lake, are affected.

According to biologist Shawn Sitar, the siscowets are markedly less fished than trout species living near shorelines. As large predators, they help regulate certain nuisance species, and they also “absorb” a portion of lamprey attacks that would otherwise prey on their “cousins.”

MSU researchers and the Michigan DNR are heading out on an expedition this month to investigate “zombie” fish in Lake Superior. https://t.co/k14lELEA0d

— WLNS (@WLNS) June 10, 2026

« Their health status constitutes a good indicator of the overall ecosystem health of Lake Superior, somewhat like a canary in a coal mine », illustrates the scientist.

Famine or Epidemic?

At the depth at which these fish reside (just under 400 meters), even the slightest environmental or trophic imbalance can have dramatic consequences. While young gray trout feed mainly on zooplankton and invertebrates, adults target small fish and crustaceans.

« Such extreme conditions involve substantial energy expenditure, so the loss of the slightest resource can lead to widespread famine », explains Sitar. « Recent blood analyses have shown that several of the zombie fish exhibited clinical signs. »

Another possibility: a disease spreading « like wildfire » through the Lake Superior siscowet populations, which further epidemiological analyses could confirm.

Earlier, zombies of a completely different kind had been reported by Colorado residents: rabbits endowed with tentacles.