ONE of the "most important" sea trout populations in the UK could be severely "imperilled" if Eton College’s plans for a 3,000-house new town go ahead, it has been claimed.

The Bevern Stream, which runs through much of the southern part of the proposed development site in East Chiltington, is part of the River Ouse catchment area and a nationally important spawning ground for sea trout.

There is discontent around the boarding school's plans, which owns a 500-acre site on the edge of the South Downs National Park.

According to the Ouse and Adur River Trust, sea trout are genetically the same as brown trout but going to sea gives the trout access to a much richer source of food.

This means sea trout are often substantially bigger than resident brown trout in the same river, and the sea trout spawned in the Ouse catchment area – and particularly the Bevern – are the largest.

They are considered very important as a species because, although relatively rare, their presence indicates a healthy river system.

Chalk streams are some of the planet’s rarest habitats and 85 per cent of them are found in England. Of the 260 true chalk streams on Earth, 224 of them run through the English countryside – but they are extremely vulnerable.

The Argus: Bevern Stream is used by the trout Bevern Stream is used by the trout

Sam St. Pierre, vice chairman of the Ouse and Adur River Trust, said: “Sea trout like to spawn in small gravelly streams and the Bevern is the most prolific spawning ground in the area.

"Sea trout from the Ouse grow to be enormous fish – even 12lb fish are not uncommon.

"This makes the river unique; if you go to rivers elsewhere, such as Wales or Scotland, the sea trout aren’t nearly as big.

“If the Bevern got further polluted, the trout here could disappear – they could just go extinct in this particular stream.

"And we’re not talking about acute pollution – we’re talking about the kind of general low-grade pollution that you would get as run-off from urban development.

"If it degraded the spawning area, the sea trout could just disappear and a vitally important sea trout population could be wiped out."

It comes as Eton College was accused of "greed" over the controversial plans to sell off land it owns in the countryside to make way for 3,000 homes.

Furious opponents have set up a protest group called Don't Urbanise The Downs, saying the plans would cram 6,000 new people into just 20 per cent of the parish.

They said the site would have a "deadly impact on the fragile ecology" of the National Park.

A spokesperson for Welbeck Land, working on behalf of Eton College said: "As a responsible promoter of sustainable places we have appointed an independent ecological consultant to carry out a full suite of surveys at North Barnes Farm.

"These surveys can take up to a year to complete.

"The results will influence our proposals and we will be working to protect and enhance the existing environment, land and waterways."