Environmentalists have found evidence that otters are flourishing in the north Pennines, despite the freezing weather conditions.
Staff at Moor House-Upper Teesdale National Nature Reserve have found the tracks of a family of three of the elusive mammals in deep snow.
Experts are keeping the location of the "exciting find" a secret.
The reserve extends from the upper edge of the Eden Valley in Cumbria to High Force waterfall in County Durham.
Reserve manager Chris McCarty said: "Otter populations are difficult to monitor because they are very shy creatures.
"Usually our only clues that otters are living in an area are the signs that they leave behind.
"Because of this we were naturally very excited by the discovery of a clear set of tracks showing an adult otter and two babies.
"There were three sets of paw-prints left in the snow, and we could even see the marks made by the tails of two of the animals as they slipped into the water.