That neon blue colour you see on the photograph is what is called 'blue waves' or bioluminescence. Since Thursday, this spectacular vision on the Juhu beach has stunned many.

When Abir Jain (20) and Nilesh Mane (22), both third-year BSc zoology students from Bhavan's College, received a call from a friend on Sunday, they thought she was trying to play a prank on them.

Understandable. For, this is the first time, bioluminescence is being reported from Mumbai. It has been reported in Lakshadweep before.

"But when she, Sayli Bhalekar, who stays in Juhu Koliwada, sent a small video to us, we realised that she means business and reached the beach around 8 pm. We were left mesmerised," the duo said.

"Wherever we placed out feet, the surrounding area started glowing. It was like watching an animation film," they said.

"We asked a few people on the beach to confirm whether it was real. We had never witnessed something as spectacular as this before," said Mane, a resident of Andheri, who volunteer for several wildlife projects. Some local residents said they have been seeing this since Thursday, he said.

The next step was to capture the visual beauty on camera.

"This was the most difficult thing as it was not possible to spot the glow from the road due to the lights. Hence, we had to move towards the Danda side, which was dark and we could see the bioluminescence clearly. I waded chest-deep in water and after making several changes to the settings on my DSLR camera, we were able to click the images," said Mane. He also believes that the El Niño effect could be one reason.

Both Abir, a resident of Goregaon and Nilesh, couldn't think of leaving the spot and they were at the spot till 2.30 am.

From what they have studied in textbooks and from what they searched on the Internet, they confirmed that it was due to phytoplanktons.

Phytoplanktons are tiny organisms about 0.5mm in size. When washed ashore, as tides vibrate, a protein called luciferase is activated, triggering a series of chemical reactions that produce the neon blue glow.

"They have a tail-like structure called flagella that produces light when disturbed, stressed or in high-pollution levels and will give a light flash lasting a fraction of a second. We identified the likely species to be noctiluca scintillans," said Jain.

The two have collected water samples from the spot and are planning to publish a scientific paper about Blue Waves.

They said they have only seen this in pictures taken in Australia and other places.

Dr Parvish Pandya, associate professor, zoology department and vice principal of Bhavan's College, said that such an activity has never been recorded or reported so far in Mumbai, though it has been reported in Lakshadweep.

"As soon as these students informed me on Monday about this activity, we went to the beach stretch that evening but did not see any luminescence. We have asked the locals to alert us when they spot it again. I appreciate the work done by these students as they are doing this research even as they are appearing for their ongoing internal examinations," he said.