For a full report on the project and a discussion of it's likely impact on migratory fish check out yesterday's Saving Species on Radio 4.
It was a good programme, well worth a listen and fairly balanced in it's approach to the reintroduction of a recently extinct native species.
I'd be more inclined to favour this project if our rivers were in good heart and were able to take more in stream barriers but that isn't the case, it's far from it in fact.
Benefits of beaver dams such as slow release of rainwater and their function of stripping sediments and nitrates are referred to on the programme but I'm not convinced.
Check it out for yourself
here