Pike anglers in the Lake District are being asked for catch reports, to help scientists work out whether pike are getting smaller.
Once a noted big fish water, Bassenthwaite rarely now produces anything over low doubles.
Scientists at the Centre for Ecology and Hydrology want to study anglers logs, to compare catches with those from a few years back.
Paul Burnell, from the Lake District National Park Authority, said: "Because pike are top of the food chain, they're a good indicator of the health of the lake.
"If changes are taking place it is essential we find out more.
"The centre wants to compare fish caught in 2007 with previous catches to see if there are any significant changes in fish populations.
"We want to know what’s happening to our freshwater species. We are asking anglers to send us catch information for 2007 and we are very keen to contact people who have kept their previous years’ records.”
Letters have gone out to the lake’s 150 permit holders appealing for help.
Information can also be submitted online here
"We want to work closely with our fishing fraternity and now have two angling representatives on the Bassenthwaite Forum, which brings together conservation and recreation groups to advise on the lake’s management,” said Mr Burnell.
He added if catch returns indicated a problem with the lake's fish populations, they would enable funds to be raise for a scientific study.