HIGHLAND PARK, Ill. — The sun beat down as Liz Ricketts peered over a wooden bridge on Rosewood Beach in Highland Park. Below her, a narrow stream carved through the sand, flowing from a grove of barren trees into Lake Michigan.

Through the murky water, littered with leaves, she spotted two rainbow trout lingering along the riverbed. They faced upstream, swimming through jagged rocks and a gentle current.

She scribbled her observations of the familiar scene on a folded slip of paper. But it wasn’t trout she was looking for — it was suckers.

“I don’t see any in here right now,” Ricketts said, scanning the stream with polarized glasses. “Basically, you count the suckers you see, to the best of your ability.”

Ricketts, a natural areas manager with the city’s Park District, documents white suckers for a Shedd Aquarium study tracking the species’ migratory patterns. Volunteers have monitored 17 sites along lakes Michigan and Superior for eight years.

But this year, the suckers came weeks early. An unusually warm winter left the Great Lakes with virtually no ice cover, accelerating the seasonal warming of the waters. It may have served as an early indicator for the species to begin its annual traverse upstream.

The slight change in suckers’ migratory patterns could have a sweeping impact on an already fragile ecosystem.

“There’s a real rhythm in nature,” said Karen Murchie, the Shedd Aquarium scientist who leads the project. “It could start getting thrown off.”

It’s just one cascading effect of the waning ice cover across the lakes, a product of climate change.

With little research, experts are still unsure of the precise impact. But it could set off a chain of events harming fish populations, eroding beaches and increasing toxic blue-green algae blooms.

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