Sand martins could return to a nature reserve for the first time in 25 years, thanks to a giant sand sculpture.
The 400-tonne (400,000kg) installation has been built at Spynes Mere near Merstham in Surrey.
Professional sand sculptors used dumper trucks and diggers to fill a giant mould to create the 20m structure.
Surrey Wildlife Trust is hoping that the new habitat will encourage the birds to return to nest every year.
The birds arrive in the UK in March, after spending the winter in Africa.
They dig 3ft (nearly one metre) burrows in which to lay their eggs, but have not nested at Spynes Mere for 25 years.
James Herd, project manager at Surrey Wildlife Trust, said: "Sand martin numbers have plummeted twice in the last 50 years as a result of droughts in their wintering grounds in Africa.
"In the UK, the natural nesting inland habitat along river banks has decreased as rivers pass through more urbanised areas and under roads.
"So creating this nest bank is important to protect them and give more security for the population to expand."
The bank was built by the sand sculpting company Sand In Your Eye in February, after several smaller test structures were tried in January.
Director Jamie Wardley said: "We added water to create the right mix, compacted the sand, and three to four weeks later the boards were removed, leaving nature and the sand martins to do the work of sculpting hundreds of nesting burrows."