19 August 2016 Last updated at 06:36 BST
There used to be loads of them in Malham Tarn in the 1960s, but they were wiped out by mink.
They're now one of the most endangered mammals in the country.
Jenny looks at what's so special about water voles.
One hundred water voles are being released into a lake in the Yorkshire Dales to help boost their numbers.