Hidden among the pine trees between Boat of Garten and Aviemore, secluded Loch Vaa is one of the most beautiful bodies of water in the Highlands.

But fears are growing for the future of this popular natural landmark after archaeologists revealed its water level dropped to the lowest level in at least 750 years in May.

The loch, which is fed by a spring, was estimated to have fallen by 4.5ft since September 2018.

No-one has yet been able to say why, although the Scottish Environment Protection agency has suggested that a “relatively dry” winter might be to blame.

Scottish Water, meanwhile, has rejected claims it could be responsible. It said an underground aquifer and boreholes supplying water to the Badenoch and Strathspey area were located about three miles upstream of Loch Vaa and were therefore too far away to affect it.

The historically significant depletion was confirmed when experts, who were asked to check for any impact on a crannog, or ancient fortified settlement, said they found pieces of wood that had survived since the 13th century just below the water’s surface.

Any old wood which was not underwater at the site has been long lost through exposure to the elements.

Although the water level has since returned to normal, the decrease has shocked locals who say the loss in volume terms would be tens of millions of gallons.

Councillor Bill Lobban previously called for a full investigation. “As a local councillor, it’s very concerning that water has dropped so substantially,” he said.

“While I understand this was an unusual winter I think it’s really important that other public bodies take on board a full investigation into the causes of the reduction in water levels.”

Louise Ross, who works for Highland Home Centre, and whose partner Brian O’Donnell helps run fishing on the loch, earlier said the local community had been left extremely worried by the extent of the depletion. She told the i newspaper: “It’s like someone has pulled the plug. “Obviously the water drops in summer and increases again in winter, but it’s never fallen by this much.

“One report said we’ve lost about 35 million gallons, but people here think it might be more. It’s a really important part of the community.

“It’s known for its crystal clear waters, and we’re worried.”

Meanwhile, work carried out by archaeologists and the Living On Water project has established that the crannog site survived the drop in water level unscathed.

The archaeologists also radiocarbondated timber found just a few centimetres underwater, with the birch samples dating back to the 13th century. The research confirmed a medieval phase of the crannog and also that the water level probably reached its lowest level since that time in May this year.

Crannogs were fortified settlements constructed on artificial islands in lochs. It was thought they were first built in the Iron Age, a period that began around 800 BC.

The 39-acre Loch Vaa, which lies within the Cairngorms National Park, has been flagged by the Scottish Environment Protection Agency (Sepa) as an area at risk of “water scarcity for the season ahead”.

Matthew Hawkins, conservation manager at the Cairngorms National Park Authority, said the drought may be the result of an exceptionally dry winter. He said: “The loch is fed from natural springs which are dependent on the level of the water table.

“The exceptionally low rainfall during 2018 and so far this year means the water table is also very low and this is likely to have affected the flow of the springs into the loch.”

A Sepa spokesman added: “Scotland can be vulnerable to periods of dry weather, which can result in pressure upon the environment and water users in some areas.

“The winter of 2018-19 has been relatively dry compared to long-term average conditions. “There has been some rainfall in recent weeks but as Loch Vaa is largely springfed it will not respond to rainfall in the same way that a river-fed loch would.”

A Scottish Water spokesman said there was “no possibility” of borehole works affecting the loch.

He added: “Our specialist hydrologists have advised that given both the geography of the area and the distance between the locations, there is no possibility of a groundwater connection between the boreholes and the water levels in Loch Vaa.”