Rapurutto spreads via wet gear including swimsuits

A warning from long-time crayfish researcher Japo Jussila says the deadly rapurutto fungus can travel between lakes on almost any damp equipment, including swimsuits and wetsuits.

Jussila, based at the University of Eastern Finland, told Yle that Aphanomyces astaci spores latch onto wet materials and remain viable long enough to infect new water bodies once the gear is reused elsewhere.

“Anyone who spends time in or around natural waters must take responsibility,” Jussila said. “Even swimsuits and towels can carry the spores from one lake to another.”

Finland’s Environment Institute (Syke) reports lake water temperatures are unusually high this summer, creating ideal conditions for signal crayfish growth and molting. Warmer water reduces the need for crayfish to migrate in search of cooler depths, allowing more energy for reproduction and shell replacement.

Petri Mäkinen, fisheries advisor for Häme Centre for Economic Development, Tourism and the Environment, inspected the crayfish population in Lake Pyhäjärvi in Kanta-Häme on Monday ahead of Tuesday’s nationwide opening of the 2026 crayfishing season.

“With the season starting tomorrow, this lake should produce good catches,” Mäkinen said.

Test traps yielded several large male signal crayfish—about 13 cm long—with fresh, clean shells and no visible signs of rapurutto infection.

Kanta-Häme now holds only one river and one small lake where the native noble crayfish still survives; the rest have been lost to rapurutto carried by invasive signal crayfish.

The 2026 crayfishing season runs from 21 July at 12:00 to 31 October.