A protected species in Finland since 1955 and only found in around 100 streams and rivers across the country, the freshwater pearl mussel can live up to 200 years and is dependent on clear, streaming water for its survival.

Part of their habitat was destroyed and thousands of mussels died on August 15, when forestry machines transporting timber between sites owned by the Stora Enso forestry company crossed the shallow and protected Hukkajoki stream in eastern Finland.

Police said last week that they were investigating the incident.

The company said on Monday that it had launched several measures including "suspended harvesting in all areas throughout Finland where there are restrictions under the Water Act, the Forest Act or the Nature Conservation Act".

"Harvesting has been suspended until the operational guidelines, harvesting plans and risks related to these sites have been reassessed," Stora Enso said in a press release.

"Any non-compliance that may be detected will be assessed in cooperation with the authorities".

The incident is being investigated as a serious nature conservation offence and has caused a public outcry in Finland.

Greenpeace Finland on Monday criticised Stora Enso and the forestry industry at large for inadequately taking environmental concerns into account in their operations, saying the case was not isolated but only revealed the "tip of the iceberg".

"Logging is carried out with inadequate information and guidance everywhere, including in areas protected by law", the group said in a statement.