A year after a forestry machine repeatedly drove over an endangered freshwater mussel population in eastern Finland, the full scale of the damage remains unclear — but the incident has already prompted significant changes in forestry practices.
The incident took place in Hukkajoki, Suomussalmi, when a harvester crossed the river housing one of Finland's largest freshwater pearl mussel (margaritifera margaritifera) populations. The species is highly sensitive to sediment and pollutants entering the water.
Researchers studying the mussels at the time witnessed the crossing first-hand. Biologist Myyri Sysivesi said the driver showed little concern when told about the endangered species in the water.
"He told me I could take my bra off before talking to him," Sysivesi recalled.
The research team estimated that the machine crossed the river as many as 400 times. The logging route had been planned to go directly over the mussel bed, according to Helsingin Sanomat. Avoiding the river would have required building an alternative road.
Roughly 100,000 mussels lived in Hukkajoki before the incident. At least 3,000 died immediately, while others were relocated. Some appeared to survive the move, but project manager Pirkko-Liisa Luhta from Metsähallitus said further deaths likely occurred over winter.
A new population count will be conducted this autumn.
"Although there are still many mussels in Hukkajoki, what really matters is whether they can reproduce," Luhta said, noting the species needs clean water and specific host fish to survive — neither guaranteed in Finland today.
Police are investigating the incident as an aggravated nature conservation offence, with an update expected later this year.
Forestry rules tightened
Public outcry last summer led to new safeguards.
"Metsähallitus has decided to leave a 45-metre buffer zone around all mussel habitats, and Stora Enso will no longer allow any vehicle crossings over waterways where the tyres get wet," Luhta said.
She called the changes "significant reforms" for a species that mostly lives in commercial forest areas rather than protected sites. She added that vehicle crossings harm other species, such as trout, and hopes more operators will stop the practice entirely.
Ongoing risks
Similar damage has been suspected in other mussel habitats, though the culprits have not been caught.
Luhta believes such an incident is now less likely, partly because fines for killing a single mussel have risen from 589 to 1,495 euros. But she said Finland remains behind other European and North American countries in mussel protection, having adopted its first conservation strategy only four years ago.
Finland has around 150 known mussel populations, of which about 100 have been studied. The mussels have an average lifespan of 120 years, and according to some estimates, can live up to 280 years.
"The mussel isn't just a water filter — it recycles nutrients and sustains the entire river ecosystem. It's a truly significant keystone species," Luhta said.
