An environment group says it is prepared to sacrifice a patch of green belt land to save a reservoir described as a “treasure”.

Elstree & Borehamwood Green Belt Society says it will give up some land opposite Watford Road, near The Fisheries Inn in Aldenham, if it means saving Aldenham Reservoir, in Dagger Lane.

Property company Liberty Aldenham wants to build 130 houses on the Watford Road site and in exchange, has promised to repair the dam and set up a trust to pay for the maintenance of the reservoir.

The reservoir is currently leased to Hertfordshire County Council by Safari Investments – but the lease is due to expire in September and will not be renewed.

Ann Goddard, the chairman of the society, said: “With the provisos of course that the agreement is viable and safe legally and that there is no other way to save this well-loved local treasure we are prepared to sacrifice some green belt because of the very special circumstances.”

Aldenham Reservoir was built by French prisoners of war from the Napoleonic wars in 1795 and is linked with Lord George Murray’s optical telegraph station on Woodcock Hill.

It was a landmark for aircrafts on both sides in the Second World War and Mrs Goddard says it should be classed as a “national treasure”.

The reservoir is used almost every day by the Verulam Angling Club and Aldenham Sailing Club, who would be without a home if it were to close.

Last week, sailing club member Jim Strother said closing it would spell “disaster”.

Mrs Goddard added: “It is beautiful. I catch my breath every time I round the bend on the Watford Road and see that shining expanse of water.

“We don’t have Windermere or Ullswater but we do have Aldenham Reservoir. Let’s keep it.”

In a statement, Hertfordshire County Council said: “We have responsibilities as lease holder of Aldenham Reservoir until 2015.

“After that time these responsibilities will transfer to the landowners and it will be for them to decide on its future.”

Safari Investments has not responded to requests for a comment.