...they stand up on their hind legs like the one in the top photo, and scent the air. This pose reveals their paler ventral (belly) fur that helps camouflage them from underwater predators such as pike.
This was a really big vole; I'd say as large as a guinea pig.
This blog charts the fortunes of water voles in and around the Whitchurch area, North Shropshire. Water voles are one of the UK's most threatened mammals, extinct in many counties, and so it's vital they receive as much monitoring and protection as there is going. Here in Whitchurch we're lucky enough to have them right in the middle of town - how cool is that?