Scientists are hunting the origins of silt which is endangering wildlife in a lake in Cumbria.
Bassenthwaite Lake is a Site of Special Scientific Interest
Bassenthwaite Lake is home to one of the UK's rarest fish, the vendace, but increasing amounts of sediment are silting up its breeding ground.
Containers are now in place in streams and becks flowing into the lake.
These will capture samples of river sediment from surrounding fields and fells. Once established where it comes from, steps can be taken to prevent it.
Bassenthwaite Lake is a designated Site of Special Scientific Interest and National Nature Reserve.
Professor Barbara Maher, from Lancaster University, said: "Each waterway has very different magnetic fingerprints making it possible to identify the major culprits.
"New scientific approaches can be used to contribute to our understanding of how sediment moves from the fells to the lake.
"Once the trouble spots are identified, they can be dealt with."