A “catastrophic” sluice failure on the River Kennet at Hungerford prompted a major fish rescue operation over the bank holiday weekend.
The sluices that failed are an historic structure linked to the former milling operations at Eddington.
Their function today is largely redundant as there is no longer an active mill.
However, the structure also fed water into a fishing lake and side stream which is supposed to flow into a Special Area of Conservation around the water meadows.
The meadows support some of the best known populations of the rare Desmoulin’s whorl snail in the UK.
The tiny snails rely on ditches and depressions in wet meadows in order to survive.
Reports of dramatic drops in the water level and dead stranded fish in the side stream prompted the Environment Agency to send an emergency team to Eddington Bridge.
They were able to recover and move several hundred trout and grayling from the stream by A4 Hire.
A spokeswoman for Action for the River Kennet (ARK), Charlotte Hitchmough, said conservationists generally did not favour sluice gates in a chalk stream because they slowed the flow and caused sediment deposits.
Ironically, the sluice failure is improving the water quality.
She said: “In many ways the collapse of the sluices has a very positive impact on the river environment – the upstream section is now flowing freely and the river is reverting to its natural course.
“However, it’s important that flow in the stream leading to the water meadows is restored, to prevent further ecological damage and to protect the habitat on the meadow.”
The chief executive of the Town and Manor of Hungerford, Jed Ramsay, agreed: “As a land and riparian owner upstream and downstream of Eddington Mill, we have seen the short-term impact of the failure of the sluices on our waters.
“However, we recognise that there will be some great long-term benefits for the environment and we are working closely with our neighbours and respective agencies involved to ensure the best outcome now and for the future.”
The repair, replacement or even removal of the sluices is likely to be both complicated and expensive, with several agencies working with the landowners involved to identify the best solution for residents and the environment.