Otters are increasingly being spotted on the River Wear thanks to a project to create homes for them.
Here are seven facts about the European species of the mammal:
1. The otter is part of the same family as badgers, weasels, stoats, pine marten and mink.
2. Otters have large lungs and can slow their heart rate down, which means they can remain under water for up to four minutes.
3. They make homes - or holts - in dense scrub next to water, in holes created by tree roots or in piles of loose logs.
4. As part of the laws protecting the species it is an offence to keep, transport, sell or exchange an otter.
5. In addition to fish, they also feast on eels, frogs, crabs and will also eat birds, either caught on the shore or in the water.
6. The biggest threat to them is the destruction of the habitat by humans and pesticides running off farmland and polluted watercourses - as well as being run over by vehicles on roads and paths.
7. They have a high-pitched squeak when calling to each other and also use a whickering, when they make a loud chatter as they get angry.