For a salmon pushing upstream, a hydropower dam is simply the end of the road. Concrete and turbines replace the river’s current, and the spawning grounds beyond — sometimes hundreds of miles away — become unreachable.
Across Sweden and Finland, hydropower infrastructure has fragmented rivers this way for decades, quietly cutting migratory fish off from the habitat they need to reproduce. Now, something is beginning to change along some of those waterways.
Rivers divided: how hydropower disrupts fish migration
Hydropower plants aren’t designed with fish in mind. Built to capture the energy of moving water, they introduce hard physical barriers into river systems — barriers that migratory species like Atlantic salmon and sea trout can’t cross on their own. For these fish, unobstructed river corridors are non-negotiable: they depend on them to reach specific upstream spawning grounds where they reproduce and where the next generation begins its life.
When a river is fragmented, the consequences compound. Fish that can’t reach spawning grounds don’t reproduce, and populations that can’t recover gradually decline. Across Sweden and Finland, where hydropower infrastructure spans multiple river systems, this dynamic has played out quietly for decades — the ecological cost of energy generation absorbed by the rivers themselves.
Engineering a passage: what fish ladders actually do
A fish ladder doesn’t eliminate a dam. What it does is create a workaround — a series of stepped pools built alongside or through a dam structure, each at a slightly higher elevation than the last. Fish swim incrementally from pool to pool, resting between efforts, until they’ve bypassed the barrier entirely. Designers must account for water flow rates, the physical capabilities of the target species, and the behavioral tendencies that determine whether fish will actually use the structure.
At Stornorrfors on Sweden’s Ume River, Vattenfall operates one of the more substantial examples of this infrastructure. The fish ladder there stretches 300 meters and has been in operation since 2010. In Finland, fishways have been constructed at Hietamankoski and Leuhunkoski on the Kymmene River. Each installation reflects the site-specific demands of its waterway and the populations it’s meant to serve.
Over 10,000 salmon in a single season: measuring real results
Numbers can be elusive in ecological restoration, but the Stornorrfors ladder is generating concrete data. In 2025, more than 10,000 salmon and over 400 sea trout passed through the structure on their way to spawning areas in the river Vindelälven. That figure represents not just successful passage, but reproductive opportunity restored — fish reaching habitat that had effectively been off-limits.
The work at Stornorrfors has also expanded beyond upstream movement. Additional measures have been taken to facilitate migration in the old riverbed downstream of the hydropower plant, addressing the return journey for salmon and trout kelts after spawning. Downstream passage is often overlooked in fish migration discussions, yet it’s equally critical to population health.
To sharpen future efforts, Vattenfall is collaborating with the Swedish University of Agricultural Sciences (SLU) to study how downstream passage at Stornorrfors can be further improved. Without systematic data collection, it’s difficult to know whether population recovery is genuinely on track or whether the numbers reflect a temporary uptick. Research partnerships help translate observed passage counts into longer-term assessments — and that kind of monitoring matters.
Finland’s next step: planning a fishway at a shared dam
Across the border, a different project is taking shape — more slowly, but with similar intent. In Finland, Vattenfall is working with the Finnish state to plan a fishway at a dam that both parties jointly own and operate. The dam currently divides flow between the artificial Lake Hirvijärvi, where Vattenfall runs a hydropower plant, and the original stream that bypasses the lake.
A constant flow is already being maintained in that original bypass stream, which represents a partial ecological concession. Flow alone isn’t enough, though. Fish can’t currently migrate through it, and the planned fishway would restore migration corridors for local fish populations in the area.
The project is still in the design phase and doesn’t yet have a permit — a detail worth noting. Regulatory approval for infrastructure of this kind can take years, and the permitting timeline reflects how complex the legal and environmental review process tends to be for projects that alter water management at shared facilities.
Balancing energy production with ecological responsibility
Vattenfall describes biodiversity and nature protection as a priority within its environmental policy, with fish migration identified as a concrete focus area. Fish ladders are one mechanism through which energy producers can begin to offset the ecological footprint of infrastructure that has been in place for generations. They don’t undo the original disruption, but they reopen possibilities that had been closed.
What the Stornorrfors results and the Finland planning work suggest together is a gradual but real shift in how hydropower operators are approaching their relationship with river ecosystems. Collaboration between energy companies, research universities, and government bodies is increasingly part of that picture — a recognition that meaningful ecological outcomes require more than engineering alone.
The projects underway are worth watching. Whether passage numbers at Stornorrfors continue to grow, whether the Finnish fishway clears its regulatory hurdles, and whether similar investments expand to other river systems will all serve as indicators of how seriously the industry is prepared to follow through.
