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26.10.2026
A research diver surfaces during a project to relocate thick shelled river mussels at Kirkonkylänkoski on the Keravanjoki river in 2025.
Gasgrid is surveying the habitats of protected mussels along the route of the future hydrogen infrastructure as part of a comprehensive environmental impact assessment process. Other impacts on nature and humans’ living environment will also be carefully assessed before the routing plans are finalised.
The environmental impacts of Gasgrid’s national hydrogen infrastructure will be carefully assessed before the routing plans are finalised and construction is planned. The thorough assessment also covers water bodies, where, among other things, potential habitats of protected mussel species along the planned routes will be identified.
“The surveys focus on two species of freshwater mussels protected in Finland: the thick shelled river mussel and the freshwater pearl mussel,” says Juha Syväranta, Senior Specialist at Alleco Oy, a company specialising in underwater research.
Along the approximately 1,500-kilometre stretch of hydrogen infrastructure from Tornio to southern Finland, more than 100 sites have been identified where mussel populations will be studied through field surveys.
“Both the thick shelled river mussel and the freshwater pearl mussel need flowing water, so the survey sites are generally rivers and streams,” Syväranta notes.
Alleco’s researchers explore the selected sites by diving, snorkelling or wading. The choice of method is influenced by factors such as water depth, current, and visibility. ”In clear water, mussels can be surveyed from the surface using, for example, an aquascope. In murky water, however, visibility is often so poor that we have to carefully feel our way along the bottom,” says Juha Syväranta.
The number of mussels is usually estimated based on samples taken from selected locations. To this end, for example, diving lines are set up across the river at regular intervals and marked with lead ropes that are lowered to the riverbed.
“The research diver follows the ropes and collects the mussels they find along the line. Species identification is performed on the surface. After that, the mussels are returned to their natural habitat,” Syväranta explains.
As a rule, disturbing protected species is prohibited in Finland under the Nature Conservation Act. The mussel survey to be conducted along the hydrogen infrastructure has been granted an exemption by the authorities.
Syväranta predicts that thick shelled river mussels, with populations across southern and western Finland, may be found along the hydrogen infrastructure.
“It is less likely that freshwater pearl mussels will be found. They usually live in clearer upper reaches of small streams with gravel beds,” Syväranta explains.
Jenni-Julia Saikkonen, Gasgrid’s Permitting Manager, says that the results of the mussel surveys will be carefully taken into account when planning the routing of the hydrogen infrastructure. A case-by-case approach will ensure that protected species are not harmed.
“It may be possible to slightly re-route the pipe to another location. In some cases, relocating the mussels may be necessary,” says Saikkonen.
It is also possible to lay the hydrogen pipeline under a body of water using so-called trenchless technology, which does away with the need to dig and make changes to the watercourse.
“The goal of the construction work is to minimise the impact on rivers and streams.
If necessary, impacts can be mitigated locally by scheduling work outside the spawning season for migratory fish or the nesting season for birds, for example,” Saikkonen adds.
Mussel surveys are part of the statutory environmental impact assessment (EIA) process, which is required before a major construction project can begin. The scope of the EIA process is reflected in the fact that Gasgrid has engaged four consultancy firms to carry them out between 2025 and 2027.
The assessments make use of topographic maps, aerial photographs, and other existing geographic data, among other sources.
“This allows us to identify, for example, potential flying squirrel habitats along the route, which are then studied in more detail through field surveys,” explains Jenni-Julia Saikkonen.
In addition to the environment, the studies take into account the impacts on people’s living conditions and quality of life.
“We will also assess any potential impacts on archaeological cultural heritage, as well as on the landscape and cultural environment. For example, EIA teams include archaeologists who investigate ancient remains located along the route,” Saikkonen says.
The environmental impacts of the hydrogen pipeline mainly take place during construction, when the pipes are buried in the ground. This is particularly evident in forested areas where trees need to be cut down along the pipeline route.
The construction work will require a 40-metre-wide area in the farmland and a 35-37-metre-wide area in the forest, but Gasgrid’s permanent right-of-way is only 10 metres wide. The rest of the area can be reforested after construction is complete.
“We can reduce the number of trees that need to be cut down by prioritising farmland when planning the route,” Saikkonen notes.
Text: Matti RemesPhotos: Juha Syväranta/Alleco Oy
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