One is an image of two Argali - horned mountain sheep - squaring up for battle. Picture here and below provided by Elena Miklashevich

When the Soviet authorities dammed the giant Yenisei River to generate hydroelectricity, they made an artificial reservoir some 388 kilometres long (roughly the distance from New York to Washington DC), never wider than 15km, and with a maximum 105-metre depth.

In doing so, ancient petroglyphs were submerged forever.

Or so scientists believed.

Now, due to markedly varying water levels in Krasnoyarsk Reservoir (or Sea), some of the submerged rock art is reappearing from the deep, while other finds are being made - thanks to observations by boat from the water - high on cliff sides.

'The highest concentration of carvings is on the rocks of the Oglakhty mountain range (left bank of Yenisei) and and Tepsey (right bank of Yenisei and the right bank of Tuba River, where it flows into Yenisei)'.

The latter, intriguingly, are on rock faces that would be impossible to reach for modern man except, perhaps, with state-of-the-art climbing equipment.

One is an image of two Argali - horned mountain sheep - squaring up for battle.

These are among a stunning neolithic art gallery found - and re-found - on shoreline cliff rocks.

The reservoir covering 2,000 square kilometres was created with the construction of the Krasnoyarsk concrete gravity hydropower dam between 1956 1972.

Due to markedly varying water levels in Krasnoyarsk Reservoir (or Sea), some of the submerged rock art is reappearing from the deep, while other finds are being made - thanks to observations by boat from the water - high on cliff sides.

Soviet scientists did their best to record the array of rich petroglyphs before they were submerged by a reservoir that stretches almost the entire distance between the Siberian cities of Abakan and Krasnoyarsk.

Expert Elena Miklashevich, an archeologist at 'Tomskaya Pisanitsa' museum-reserve, said: ‘Dozens of ancient rock art sites were submerged.’

At the time, there was an understandable belief that this superb treasure trove was gone forever.

Now, though, many masterpieces have emerged from the deep, and proved resistant to decades of water, while highly significant new discoveries have been made as scientists scour rock faces from the surface using binoculars.

'It turned out that many petroglyphs, probably more than half of the known ones, were not totally destroyed under the water.'

'In the 1990s, when problems began in the Russian economy, the level of the Krasnoyarsk reservoir began to fall quite often,' the lecturer explained.

'Sometimes in the southern part of the Yenisei River, it was almost back to its pre-flood level,’ she said.

'In the 1990s, with my first independent expedition, I conducted documentation of petroglyphs in the Oglakhty mountains, 60 km north of Abakan.

'Suddenly we saw that islands had appeared in the middle of the reservoir: the water had fallen very low.

Scientists were to use climbing equipment to research some petroglyphs in 1960s. Picture: Yakov Sher

'We went to inspect the rocks along the coast and it turned out that many petroglyphs, probably more than half of the known ones, were not totally destroyed under the water.

'Some were hidden by scree, others destroyed, but still, a lot of them were available for copying.’

By 2014, funding was given by State Nature Reserve Khakassky for a more detailed inspection.

'The petroglyphs are located along both banks of Yenisei River and its tributaries between Abakan and Krasnoyarsk,’ said Dr Miklashevich.

'In the central and northern parts of the reservoir, where the water level remains high even when it is discharged, some rock art sites are located 40 metres underwater.’

They are unlikely to be seen again.

'It is never easy when pictures are made from the ground, let alone taking them from a shaking boat.'

'But in the southern part (from Abakan downstream), luckily, the water level drops so low that the rocks on the riverbanks open - and the petroglyphs can be seen.’

This gives the opportunity to study and record these ancient art works.

Dr Miklashevich said: 'The highest concentration of carvings is on the rocks of the Oglakhty mountain range (left bank of Yenisei) and and Tepsey (right bank of Yenisei and the right bank of Tuba River, where it flows into Yenisei).

'The study of these petroglyphs is very important - modern methods help find new important details of the compositions, and new figures.

'More interestingly, absolutely new engraving areas, not spotted before, are being found.

'Earlier, they were probably covered with lichens or located too high to see them.

Engraving of the wild bull-aurochs, now extinct in this area, dated allegedly as 5,000 years old.

The research can be hazardous and ‘risky’, she said.

'Scientists sail in boats close to the rocks, clean the surface…and standing in the boat take pictures…’

'It is never easy when pictures are made from the ground, let alone taking them from a shaking boat.’

Significant fluctuations in the water level - by as much as six metres - mean that the experts can sometimes see rock art emerging from the depths, but also notice petroglyphs higher up cliff faces.

'We have spotted a number of very interesting multi-figured compositions,’ she revealed.

Large multi-figure composition in Ust-Tuba.

Advances in technology, not least photography, mean the previously-known images can be looked at afresh with far more detail recorded and understood.

'We find new features in the style and technique of drawing,’ said the archeologist.

'Every detail is important - how the eye is located, the way the hooves are drawn, in order to distinguish the style or hand of the master.’

Scanning the rock faces from the water using binoculars, the scientists have found many new petroglyphs.

Before the flood 'it was impossible to see them from the shore’.

She revealed: ‘We made the great discoveries. On the rocks of Oglachty a whole new site was found.

'One of the brightest finds here is (rock art) depicting Argali (mountain sheep), а, and wild bulls.'

Wild boar from Ust-Tuba.

The image of the wild sheep squaring up is seen as unique.

'In Ust-Tuba, we managed to find an image of a bird - not previously known among the ancient petroglyphs of the Yenisei area, but well-documented among similar images in the Mongolian Altai Mountains.

'A real success was the discovery in the Ust-Tuba large multi-figure compositions, where all the animals are presented in pairs - wild bulls, sheep, goats, horses, deer, elk, and wild boars ...

'Many images here are engraved and polished.’

Most of these are impossible to reach, which means close up copying is not possible.

The image of the wild sheep squaring up is seen as unique.

'The only way to study them was to photograph them from the boat, using full-matrix camera and telephoto lens,’ she said.

'At least we can see the basic details of the drawings,’ she said. 'All the animals are wild.

'Many of those engraved on the rocks do not live in these places any longer: some have become extinct, others have changed their habitats.

'All of these drawings are clear witnesses of a different nature and landscape (compared with the time when they were made).’

Images of wild horses now extinct in this area.

She admitted: 'Scientists do not know how to accurately date these images.

'It is clear only that they go far back. The earliest known and accurately dated petroglyphs in the Yenisei area are three to four thousand years old, but these are definitely older.

'Yet there are no archaeological anchorages. The best possible solution is to analyse the species and link them to some climatic period.’

So the question remains: if these petroglyphs - circa 5,000 years old - are unreachable for modern man, and visible only by boat on an artificial reservoir, how were they drawn by prehistoric artists?

How did ancient man clamber to his canvas?

The rocks here are sandstones, siltstones, tuffites, limestones, and dolomites.

Image of a moose found close to the shore in Oglakhty.

She believes that thousands of years ago, these sites were easier to reach.

‘When the artists made the drawings, the configuration of the slopes and the rocks themselves was different,’ she said.

'There were some ledges on which the artist could stand.

'And below there were other levels of rocks located as steps.

'Since it was very long ago - at least 5,000 years - there have been changes at the geological structures.

'The lower tiers collapsed, exposing new rocky surfaces on which artists of subsequent epochs applied images.’