Mr and Mrs Beaver are part of an experiment by Kent Wildlife Trust to see if this species can be reintroduced to the wild. Beavers died out in Britain some 500 years ago. They are large animals - the size of a well-fed Labrador - but you will be lucky to see more than a black nose swimming along the stream. Ungainly on land, they are happiest in water; a rustle of reeds and a ripple on the surface of the stream are the only things to announce their presence. They take a dip as soon as they hear anyone coming. They can hold their breath underwater for a quarter of an hour.