The Nagas or the Snake people were the natural enemies of Garuda, the mount of Lord Vishnu. 

Garuda was a huge and magnificent bird and was extremely powerful. So powerful that Lord Vishnu had himself requested Garuda to become his mount. 

During his childhood Garuda's mother – Vinata had been a slave to Kadru, who was the mother of the Snakes. 

As the snakes had ill-treated Garuda in his childhood, on growing up, Garuda wanted revenge. Garuda asked a boon from Lord Vishnu that the Nagas were to be his natural food. 

Garuda was powerful – phenomenally so. 

After he received a boon from Vishnu, Garuda nearly massacred the Nagas. It went so bad that the Nagas feared that they would be exterminated by Garuda. 

So the Nagas made a deal with Garuda that they would send a Naga as tribute and in return, Garuda would not indiscriminately hunt the Nagas. 

Garuda naturally agreed to this condition. 

Once, however, Garuda was unable to stop himself as he saw some Nagas hiding under the waters of Kalindi. (This is another name for the Yamuna river.)

Unknown to Garuda, a great sage called Saubhari was meditating inside the river.

The attack of Garuda on the Nagas inside the river caused great disturbances in the water. So much so, that Saubhari was disturbed from his meditation. 

The great sage opened his eyes and was furious that his meditation had been disturbed. 

Angrily, he pronounced a curse on the bird. "The minute that bird steps into this lake for its food again, it shall die."

Garuda heard the words of the sage and slunk away from there.

Unfortunately, it was not just Garuda who heard the words. Another Naga called Kaliya heard the curse too.

Kaliya was a venomous Naga and extremely powerful and he was arrogant too.

During one of the times that the Nagas paid "tribute" to Garuda, Kaliya came to the place and gobbled up the other Nagas, before Garuda could get there.

Garuda was naturally infuriated with this. 

There was a massive battle between Kaliya and Garuda and naturally Kaliya lost. 

In fact, Kaliya just escaped with his life. Just about.

Deciding that he just could not fight with Garuda and win, Kaliya along with his wives moved his residence. And he smartly moved to the one place that Garuda could not come – the Kalindi river.

But Kaliya could not forget his defeat and he nursed a hatred – a hatred for all creatures and not just Garuda.

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The Gopa boy led his cow to the river and the heat in Vrindavan was really bad. 

Unable to stop itself the cow ran towards the water and without even pausing the cow drank the river water.

A few seconds later, the Gopa boy was horrified. 

His beloved cow had slumped dead.

That was when the Gopa saw the water and was even more horrified. The fishes, the plants of the place were all lying dead. The poison wafting from the river was so powerful that even the bird which flew above the water fell inside the water, unable to bear the noxious poison fumes emanating from the water.

Panting and gasping for breath, the Gopa ran. 

And he ran straight towards the one person whom he knew would help.

***********

Krishna's lips grew in a thin, grim line as he heard the boy's story.

"I will take care of this." Krishna said pushing aside the boy.

"Krishna, take Balarama with you." The Gopa boy screamed in horror as he saw that Krishna had started walking away from the place.

"Stay here." Was all Krishna said as he walked away.

**********

In fifteen minutes flat, the entire village was screaming and moaning in fear. They just could not believe what Krishna had done. None of them could even control themselves as they all ran towards the river, nearly paralysed in fear.

Yashoda nearly jumped inside the river as Balarama angrily pushed her back.

"My son..." Yashoda wailed as she saw Balarama who just refused to let her go any further.

"That is Krishna." Balarama said in a calm tone. "Nothing can happen to him."

*********

Krishna had done exactly what was expected of him. Listening to the Gopa's story, Krishna was determined to teach the Naga inside the river, a lesson.

He climbed on top of the tree and without any further thought, jumped into the river.

The poison of the river should have killed any normal human, but Krishna was not even affected, as he went deeper inside the river.

In the deepest part of the river, he found Kaliya. (There is a folk story that the wives of Kaliya first saw Krishna, because Kaliya was asleep when Krishna swam inside. Kaliya's wives were determined to save the child and asked him to leave before Kaliya woke up. But then that did not work, because Kaliya woke up in the middle.)

There was a massive fight between Krishna and the Naga – the likes of which, had never been seen before. (During the fight with Krishna, Kaliya is said to taken the form of a multi-headed snake.)

First, the Naga squeezed Krishna threatening to suffocate the little boy. 

Krishna escaped the clutches of the snake and swam away, trying to make sure that he never stayed away from the vision of Kaliya.

Kaliya was furious and spat poison on the boy.

Krishna step sided the attack and caught the snake by the neck. He squeezed the neck as the snake faltered and fell back.

But then the snake attacked back.

The fight between the two went on for a long time as the Gopas on the land were now feeling doomed. They were sure that no one could survive under the water for so long and they were all wailing.

That was when they saw an impossible sight.

Krishna and Kaliya both surfaced and it seemed like Krishna was dancing on the hood of a thoroughly beaten up enormous snake.

(After Krishna had defeated Kaliya, Krishna was about to kill Kaliya, when Kaliya's wives interfered. They prayed Krishna to let their husband live. Krishna relented.

Krishna asked Kaliya to go back to the seas from which Kaliya had come.

Further Krishna added that seeing Krishna's footprints on the Naga's hood, Garuda would no longer attack the Naga.)