One of the ways you can tell juvenile water voles from fully grown adults (and also from bank voles and field voles) is that young w-vs have darker fur. In fact very little ones, newly-emerged from the nest, sometimes look nearly black. It makes me think of the difference between milk and plain chocolate.
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?