I'd been watching this vole at White Lion Meadow, and when it swam off I started to put my camera away. Then something - as I thought, the vole - climbed back out of the water. It was this rat, which seems only to have one eye. The vole later reappeared further down the stream, but hiding in a clump of celandine.
I know from experience rats in any serious number can be bad news for water vole colonies, so I'll need to monitor the situation carefully. A single monocular rat probably isn't much threat on its own, but rats rarely come in ones.