A 50,000-year-old crater lake in western India has left scientists baffled after it mysteriously changed colour to pink.

Lonar Lake’s colour shift occurred over the span of a few days and became reddish-pink on June 10. The new colour lasted for 16 hours and the lake slowly turned back to its usual green.

The two videos show the difference in colour, one showing the lake's strikingly pink colour, the other shows the lake returning to its natural green.

According to NASA Earth Observatory, the colour change was probably caused by microscopic life that responded to stressful environmental conditions.

A unicellular green algae called Dunaliella salina, which is present in many water bodies, is green when “water conditions are favourable.”

Harsh conditions such as surging saline concentration of water or exposure to a lot of light may cause these algae to produce protective carotenoids, such as the orange-red beta carotene, which may turn the water pink.

The water levels at Lonar Lake depleted due to evaporation caused by the dry weather in June. That may have resulted in more salinity and triggered a change of colour is the theory.

Lonar Lake was formed 50,000-years-ago after a high-velocity meteor struck the Earth's surface.

Scientists are baffled by a 50,000-year-old meteorite crater lake that changed its colour from green to pink in west-central India.

Lonar Lake’s color shift occurred over the span of a few days and became reddish pink on June 10. The new colour lasted for 16 hours and the lake slowly turned back to its usual green.

A video taken by a local reporter shows the lake strinkingly pink on June 10, another video shot a few days later shows the pink fading out slowly.

The unusual phenomenon drew the attention of scientists around the world including NASA researchers, who are still probing the reasons for the transformation.

According to NASA Earth Observatory, the colour change was probably caused by microscopic life that responded to stressful environmental conditions.

A unicellular green algae called Dunaliella salina, which is present in many water bodies, is green when “water conditions are favorable.”

Harsh conditions such as surging saline concentration of water or exposure to a lot of light may cause this algae to produce protective carotenoids, such as the orange-red beta carotene, which may turn the water pink.

The water levels at Lonar lake depleted due to evaporation caused by the dry weather in June. That may have resulted in more salinity and triggered a change of colour is the theory.

This could be similar to Lake Urmia in Iran, where water turns red during dry seasons due to high amounts of saline and lower water levels.

Indian scientists have collected samples from the lake and are awaiting lab results.

Lonar Lake was formed 50,000 years ago by an extremely high-velocity meteor impact. It is the only “fresh” impact structure in basalt on Earth, which is similar to impact craters on the surface of the Moon.