Finnish freshwater mussels tested as natural water purifiers in Laukaa

Researchers at the University of Jyväskylä are studying whether freshwater mussels can effectively filter bacteria, nutrients, and sediment from agricultural and forestry runoff in a controlled stream environment in Laukaa, reports Finnish broadcaster Yle.

Around 600 mussels will be placed in mesh cages along Capeenpuro, an artificial 1-kilometre stream built for research purposes. Automated sensors will monitor water acidity, turbidity, conductivity, oxygen levels, and flow rate before and after the mussel cages, while students collect samples for lab analysis of nutrient reduction.

“In the lab, we’ll measure nutrient levels—hopefully they’ll decrease over the study period,” said Milka Niinistö, a student involved in the fieldwork. The mussels feed by filtering microalgae and organic particles, which also removes harmful bacteria and parasites from the water.

The project is part of broader efforts to develop mussels as a natural water treatment solution for polluted ditches, small waterways, and fish farms. Professor Jouni Taskinen noted that lab tests have already shown mussels can eliminate fish parasites, bacteria, and fungal spores that destroy fish eggs.

“Finland has many streams and small water bodies burdened by agriculture and forestry,” Taskinen said. “Mussels could offer a sustainable way to clean them.” A key challenge remains scaling up freshwater mussel farming, as wild populations cannot be harvested for such projects.

Capeenpuro, completed two years ago with funding from the R. Erik and Bror Serlachius Foundation, has also become a research site for endangered landlocked salmon. While common fish species have colonised the stream, only one salmon has been observed—a decline researcher Jukka Syrjänen attributes to genetic shifts in salmon populations over the past century, reducing their tendency to migrate.

The site is hosting international researchers this summer, including a team from the University of Zurich testing new benthic organism monitoring equipment. Marian Ofner praised the stream’s rare combination of on-site accommodation and power supply for fieldwork.