Didymo cells have been found in algae samples taken from submerged rocks and debris at two boating access sites on the Au Sable River north of Luzerne in Oscoda County.

Sampling conducted by Michigan Trout Unlimited in late April found several didymo cells at the Parmalee Canoe Launch off North Red Oak Road and one cell just downstream at the Whirlpool access off West Cherry Creek Road. No evidence of didymo was found in samples taken upstream at the McMasters Bridge Road access, farther downstream, or in a number of tributaries sampled to date.

Didymo, also known as “rock snot,” is a microscopic diatom (single-celled alga) that thrives in cold, low-nutrient streams generally considered pristine. Under the right conditions, cells can form extensive stalks, or blooms, creating dense mats that cover the stream bed and reduce habitat for macroinvertebrates, including mayfly, caddisfly, and stonefly nymphs, which are crucial food sources for fish.

Though no blooms have been observed at either of the two Au Sable River access sites, Michigan Trout Unlimited is joining the Michigan departments of Natural Resources and Environment, Great Lakes, and Energy to urge anglers and all stream users to properly clean waders, boats and equipment between every site visit.

“With trout season now open across the state … it’s important to remind everyone enjoying Michigan’s streams and rivers to take steps to decontaminate to prevent further spread of didymo,” said Bryan Burroughs, executive director of Michigan Trout Unlimited.