Across Europe during the middle ages beavers were heavily persecuted. Between the demand for their pelts and scent glands, and the flooding may caused, they were hunted for the financial incentives or merely for the problems they caused.
The problem is that rapidly it becomes apparent the good they did in the places that they have been lost from. Flash floods become far more common, and other times of the year droughts. Water quality reduces dramatically, and biodiversity along the riverbank is harmed.
In many parts of Europe one of the most stupid arguments for avoiding reintroducing beavers is that they will eat the fish- a stupid argument as they are strictly herbivores. Indeed the pools that beaver dams cause, are often fish nurseries and therefore greatly increase the number of fish in a river catchment. This is despite the fact that beavers often increase the number of otters living in the river.
Even in the UK there have been sanctioned beaver reintroductions (though of the three largest, 2 to were unsanctioned discoveries of beaver populations which were then studied and allowed to remain). the beaver population in the tay river catchment area in Scotland is now thought to number at least 400, the otter river catchment area in Devon is thought the host at least 30 beavers.
Beaver numbers in the Nordic countries are doing reasonably well having never dropped particularly low. Likewise in the North Eastern countries of Europe beavers are still reasonably common.
Throughout Western and central Europe, reintroduction projects have been held, and while these have had varying degrees of success it means that all these countries have populations numbering between the tens and hundreds.
It is quite incredible, that beavers now number more than a million, as back at the turn of the 20th century there were thought to be 1200. Indeed in 2003 the estimate for the number of wild beavers in Europe was 639000, so this recovery is still very much in progress.
Realised centuries too late, authorities across European beaver habitat, have discovered that beavers give us solutions to problems that otherwise can cost millions, and that it is therefore cheaper to deal with occasional problems that beavers cause than to live without their presence. As ecosystem engineers, beavers vastly improve the health of rivers. Biodiversity is much higher in rivers with beavers in existence, rivers tend to meander more and carry less sediment down to the sea. River courses tend to be more permanent,and support greater amounts of vegetation along its banks.
The return of the Beaver to European rivers, and indeed to British rivers is a clear positive and must be treated as such. There will be occasional issues, and the appointment of beaver consultants is entirely sensible as has happened in various parts of the UK. Funding their work, to counteract beaver problems will save huge amounts of money in other places.