Water vole numbers are tumbling across the country, with an estimated 90 per cent decline in population in the last decade, as a direct result of the populations of North American mink which established themselves in the wild here in the 1950s and 60s after escapes from fur farms.
In many river catchment areas the small swimming rodents, once a familiar sight, have been wiped out completely.
"Wherever there are mink, water vole numbers reduce dramatically," said Ian Davidson-Watts, Hampshire downs and rivers officer for English Nature, the Government's wildlife service. "They are a favourite item of mink food. It's like giving a mink a McDonald's."
Unfortunately the weekend mass mink release was in the valley of Hampshire's River Avon - which until now has had one of the healthiest remaining water vole populations in the country, partly because mink in the area are strictly controlled by gamekeepers.
"The Avon water voles will be hammered now, as will the waterfowl and the ground-nesting birds with their second broods," said Mr Davidson- Watts. "Most of the released mink won't survive, in fact they will die a horrible death of starvation - their mothers haven't taught them to look after themselves - but they will trash the local wildlife in the process. They can range 20km in a day."
The Hampshire Wildlife Trust is also concerned about the threat to water voles and birds, possibly waders along the New Forest coast, where the mink may spread. It is concerned, too, that public over-reaction to the release may threaten the otters that are just coming back to the Hampshire Avon after 10 years of conservation work.
"It would be absolutely dreadful if any otters were trapped or poisoned or shot by over-zealous people who were trying to control the mink," said conservation officer Debbie Wicks.