The animal was hunted to extinction around 400 years ago and had been regarded as a missing element of the countryside.
However, with the Scottish Beaver Trial, launched in May 2009, a handful of Norwegian beavers were re-introduced to the Knapdale Forest, Lochgilphead.
The program is due to expire in the next few months but campaigners hope the ecological and commercial benefits will lead to an extension.
Projet manager Simon Jones said: "Where you get beavers, you get biodiversity. The consequences are good for wildlife."