Conservationists in Cumbria believe they may have come up with a world first.
Environment Agency staff have been working to improve a section of river that runs through a dark tunnel - or culvert - near Seascale.
The lack of light is thought to have been discouraging fish from passing through it to the areas where they could breed.
So the Agency has come up with a rather unusual solution.
Our Rural Affairs Correspondent, Tim Backshall reports:
It is hoped that a new batch of river sky-lights will help fish migrate in west Cumbria.
The innovative lights have been created as part of a water quality and biodiversity improvement project at New Mill Beck.
The project work, which was carried out by the Environment Agency, has lifted the lid on a 50 metre section of culverted beck where the River Calder meets the Irish Sea.
The site is home to Natterjack toads and removing the culvert will improve the habitats for migrating fish.
It is designed so that the fish swim in the right direction and navigate towards the light.