Thousands of American gizzard shad are floating belly up in Little River, but the grave looking pool of dead fish doesn't surprise environmentalists in Windsor-Essex.

Typically, shad do not swim further north than New York, but in recent years, they have been swimming as far as Canada and quickly dying, according to the Essex Region Conservation Authority.

"We've seen it happen quite commonly over the last 15 years, every two years or so depending on the thaw," said Tim Byrne, ERCA's director of watershed management services.

The problem is shad are highly prone to thermal shock, which is a sudden change in water temperature that immediately kills schools of fish.

WDR_Shad

Thousands of dead shad fish are seen in Little River. (Dale Molnar/CBC)

"It's unfortunate, but they are not a native species to this area," Byrne explained, saying fish native to the region can handle the temperature changes.

The amount of floating fish is also reflective of the species that commonly swim in large schools.

Thousands of shad died along the Belle River back in 2014. At the time, officials said the reasons for the massive death also included sewage that bypassed treatment and record rainfall.