Visitors are being urged to stay away from a popular wildlife site following the decline.
Red squirrel numbers have dropped at Shap Wells in recent months with the Penrith & District Red Squirrel Group advising people to keep clear of the area to help the remaining population recover.
The group said in a statement: “Over the last couple of months, we have suffered an as yet unexplained loss of reds at our red squirrel walk at Shap Wells.
“We are monitoring the situation and at this stage have removed a lot of feeders to help this monitoring.
“Our rangers are there regularly.
“I would ask members of P&DRSG and the public to stay away for the time being giving maximum chance for the few red squirrels left to breed successfully and build up in numbers again.
“It will also give the path through the site a chance to recover after the appalling weather we have experienced in recent weeks.”
The Penrith & District Red Squirrel Group, a registered charity since 2006, was founded in 1994 by residents concerned about the spread of grey squirrels.
The charity is dedicated to preserving red squirrels in the wild within the Penrith & District area and relies on a growing network of supporters, members, volunteers, and dedicated Red Squirrel Rangers.
The cause of the decline remains unclear.