European Water Vole infestation

In the midst of a Water vole (Arecolis amphibius, a.k.a. European Water Rat, Ratty (as in "Wind in the Willows") infestation that is wreaking havoc with our Cattails and Sweet Flag. Fortunately, they seem to be staying out of our garden for now, but for how long?

It seems to me that most on the site here are from the U.S.A., but maybe somebody has some suggestions on how to deal with them?