Heavy rain and flooding have caused water to tumble down the most famous cliff in the Yorkshire Dales for "the first time in living memory".
Water flowed over the top of the white limestone rocks of Malham Cove on Sunday, briefly making it one of England's highest unbroken waterfalls.
Footage of the occurrence has been seen online more than 100,000 times.
The Yorkshire Dales National Park said it was "struggling to find out the last time it flowed as a waterfall".
Malham Cove is usually dry as water flows through cracks and gullies to its foot before reaching the cliff edge.
Alan Hulme, head of the park's ranger services, said the water systems were so full it flowed along what has been known as Dry Valley and over the top of the cove.
He said: "The people who saw it have been very fortunate, it was just a fantastic experience."
The 80m (260ft) drop was about two-and-a-half times bigger than England's usual record holder, Hardraw Force, also in the Yorkshire Dales.
- A natural amphitheatre 300m (985ft) wide and about 80m (260ft) high
- A limestone pavement formed after the last Ice Age by melt-water, largely from Malham Tarn
- Melt-water cut back the cove as it fell over the edge as a waterfall
- The surface of the cove is characterised by limestone blocks called clints and fissures called grykes
Source: BBC Hands on Nature
Christopher Scaife was meant to be taking part in a caving club trip, but he headed to Malham for a walk after it was cancelled due to the weather.
He said: "The water usually sinks about a mile away from the top, I've never heard of this happening.
"We went to the local pub afterwards and no-one there had seen anything like it."
Mr Hulme said some people he had spoken to told him it last happened in "the early 19th Century", others in 1720 and some going as far back as the Ice Age.
"There is a lot of hearsay," he said. "We may never know."