At Strumpshaw Fen, the RSPB have been trapping and humanely disposing of the mink in an attempt to tackle the problem.
"Wildlife in America has had hundreds of thousands of years to get used to mink," says Tim Strudwick of the RSPB.
"In many areas the water voles won't have that time to adapt and they'll just disappear."
Inside Out: EastView our story archive to see articles from previous series.
Find local news, entertainment, debate and more ...
Beds, Herts & BucksCambridgeshireEssexNorfolkNorthamptonshireSuffolk
David Whiteleyyour local Inside Out presenter.
Contact usContact the East team with the issues that affect you.