Residents, farmers and livestock owners are concerned about a partially dried up leat which is causing problems for cattle and ponies and other wildlife.

The manmade watercourse, created for industrial use and agricultural irrigation, usually flows all year round.

However, farmers and residents have been alarmed to see a big stretch completely dry, while where there is water, it is also very slow running and also far shallower than normal.

The Grimstone and Sortridge Leat supplies water to ten farms and two cottages near Pew Tor, off the road between Tavistock to Princetown via Merrivale. It has run dry on from the base of Pew Tor, where the road leads to Moortown and Sampford Spiney, or back to Tavistock. All of the stretch from Pew Tor to Rylands is dry.

Several farmers have written to DNPA saying the leat is sometimes blocked by members of the public and have appealed to visitors not to create their own paddling pools by damming sections.

The farmers said the DNPA responded to its concerns by promising to stage more warden and ranger patrols in the area.

The farmers said: “The leat is frequently blocked due to unauthorised damming by members of the public. Locals kindly request that visitors refrain from constructing dams to create paddling pools in this vital water source. If you encounter a dam, please remove it and photograph the area and report to the Dartmoor rangers.

“Public cooperation is essential in ensuring the continued water supply for moorland livestock, farmland and homes.”

One resident said: “The leat at Plasterdown is completely dry, which I have never seen in my 40 years of living in Tavistock. Seeing ponies and foals standing in a dry leat licking at stones was heartbreaking.

“I understood there was a water supply underneath Pew Tor and was used to top up the leat. If this is true, why hasn't this happened?

“If something isn't done soon, the ponies will soon be dying of dehydration. Plus sheep and cattle rely on this source of water. In this heat is is disgraceful that this is happening. Who needs to step up to sort out this potentially fatal issue? Farmers? Dartmoor National Park or council?”

The Grimstone and Sortridge Leat, comes off the River Walkham and runs southwesterly to the 16th century manors of Grimstone and Sortridge in the parish of Horrabridge.

Long-term Whitchurch farmer Francis Mudge is surveying the leat by driving its length in his tractor.

He said: “I’ve never know it so dry and there could be several causes, whether it’s blocked somewhere upstream or at Weir Head maybe.”

The last time he remembers it being so dry was during the famous drought of 1976 – but that was only for two days. The current spell has lasted more than two weeks.

A DNPA statement said: “We’re aware of the matter and are in contact with local farmers and stakeholders to understand the situation in more detail.”