The catchment area from the headwaters to the sea is one system for the river organisms. Routes for fish migration should be opened up, streams restored or compensatory channels created to ensure good spawning grounds. This is an imaginary freshwater system in Finland. It has several lakes and four rivers, of which one flows into the sea. How do the environmental impacts of hydropower appear in this landscape? What routes do aquatic species use to move? Where do they reproduce and how can their living conditions be improved?
1. Natural river
This inland river runs from the east into a lake. Hydropower plants have never been built on this river. The natural river splashes in the rapids and rests in the pools. Migratory fish enjoy free migration routes and suitable spawning areas.
2. Constructed river, example 1: Completely constructed river in the lower reaches.
This big river, flowing into the sea, collects its waters from all lakes and rivers of the catchment area. The entire flow of the river is harnessed to produce hydropower. The stream conditions have completely disappeared from this river. The river ecosystem now exists only under the conditions of the regulation regime. The chain of power plants utilise the largest amount of water when the need and the price of electricity are the highest. Power plant dams prevent the fish from migrating upstream and downstream.
3. Constructed river, example 2: Partially constructed river in the upper reaches.
This inland river runs from the west into the lake. Large portion of the river’s flow has been harnessed to produce hydropower, but not in all the river sections. Most of the stream conditions have disappeared. The aquatic life is largely determined by the rhythm of flow regulation and hydropower dams prevent the fish from migrating up- and downstream.
4. Restored river
This inland river runs from the south into the lake. Formerly operational hydropower plants have been dismantled or bypass channels have been build. The restored river is returning to its natural state. Opening up barriers and restoring spawning areas allow the return of migratory fish species. Life in the stream is gradually recovering.