The riverbank has an unlikely champion fighting against an unwelcome invader - the humble otter!
Experts reckon rising numbers of otters have led to a comeback for water voles on Britain's waterways.
That's because the otters are taking on the voles' big enemy, American mink, who have done well in Britain since escaping from fur farms.
But the scientists say we can't just rely on the otters, and we need to work to protect the water vole ourselves.
The number of voles in the wild has taken a big drop in the last 100 years.
As well as being hunted by mink, they have faced a struggle to find places to live.
Lots of their natural habitat has been damaged or wiped out by humans.
Otters numbers started to drop about 50 years ago because of chemicals being used to kill insects.
But because rivers are being cleaned up once more, they have started to make a comeback.