The completion of the sluice will enable water levels to be carefully managed for many years to come
The culmination of three month's work at Cornwall's largest freshwater reedbed will secure the long-term future for a wealth of wetland birds.
RSPB staff at the Marazion Marsh Nature Reserve and Network Rail's contractors have worked together to install a new sluice.
This will maintain water levels all year and prevent the pools and reedbeds from drying out in summer.
This will help to re-establish fish populations - which are essential for birds such as the grey heron.
Dave Flumm, RSPB Site Manager said: "Installing a new sluice on the railway to control water levels across the wetland site and removing years of silt from the ditch network has now been completed. This will help us stop water draining off the site in summer for the first time since the reserve was created in 1990.
"We are extremely grateful to Network Rail and Natural England who have funded the work and the contractors have done a great job."
Marazion Marsh is a Site of Special Scientific Interest (SSSI) for its wealth of wildlife and a Special Protection Area (SPA) for bittern and aquatic warbler, both of which will benefit from the work.
Dave Flumm added: 'Working on a marsh at this time of year always attracts attention and especially when heavy plant machinery is involved such as swing-shovels as they churn up the muddy ground in spite of all the precautions taken by the contractors'.
"Unfortunately the ditches were so full of silt, there was no other way to dredge them and although it will be some time before the footpath and banks grass over, next spring the site will have fully recovered and the better flows of water will help our bird and fish populations to reach new levels".