When He understood that the water of the Yamunā was being polluted by the black serpent Kāliya, Lord Kṛṣṇa took action against him and made him leave the Yamunā and go elsewhere, and thus the water became purified.
When this story was being narrated by Śukadeva Gosvāmī, Mahārāja Parīkṣit became eager to hear more about Kṛṣṇa's childhood pastimes. He inquired from Śukadeva Gosvāmī how Kṛṣṇa chastised Kāliya, who had been living in the water for many years. Actually, Mahārāja Parīkṣit was becoming more and more enthusiastic to hear the transcendental pastimes of Kṛṣṇa, and his inquiry was made with great interest.
Śukadeva Gosvāmī narrated the story as follows. Within the river Yamunā there was a great lake, and in that lake the black serpent Kāliya used to live. Because of his poison, the whole area was so contaminated that it emanated a poisonous vapor twenty-four hours a day. If a bird happened to even pass over the spot, it would immediately die and fall down into the water. Due to the poisonous effect of the Yamunā’s vapors, the trees and grass near the bank of the Yamunā had all dried up. Lord Kṛṣṇa saw the effect of the great serpent's poison: the whole river that ran before Vṛndāvana was now deadly.
Kṛṣṇa, who advented Himself just to kill all undesirable elements in the world, immediately climbed up into a big kadamba tree on the bank of the Yamunā. The kadamba is a tree bearing round yellow flowers that is generally seen only in the Vṛndāvana area. After climbing to the top of the tree, He tightened His belt cloth and, slapping His arms just like a wrestler, jumped into the midst of the poisonous lake. The kadamba tree from which Kṛṣṇa jumped was the only tree there which was not dead. Some commentators say that due to being touched by the lotus feet of Kṛṣṇa, the tree immediately became alive. In some other Purāṇas it is stated that Garuḍa, the eternal carrier of Viṣṇu, knew that Kṛṣṇa would take this action in the future, and so he put some nectar on this tree to preserve it. When Lord Kṛṣṇa jumped into the water, the river overflooded its banks to a distance of one hundred yards, as if something very large had fallen into it. This exhibition of Kṛṣṇa's strength is not at all uncommon, because He is the reservoir of all strength.
When Kṛṣṇa was swimming about just like a great strong elephant, He made a tumultuous sound, which the great black serpent Kāliya could hear. The tumult was intolerable for him, and he could understand that this was an attempt to attack his home. Therefore he immediately came before Kṛṣṇa. Kāliya saw that Kṛṣṇa was indeed worth seeing because His body was so beautiful and delicate; its color resembled that of a cloud, and His feet resembled lotus flowers. He was decorated with Śrīvatsa, jewels and yellow garments. He was smiling with a beautiful face and playing in the river Yamunā with great strength. But in spite of Kṛṣṇa's beautiful features, Kāliya felt great anger within his heart, and thus he grabbed Kṛṣṇa with his mighty coils. Seeing the incredible way in which Kṛṣṇa was enveloped in the coils of the serpent, the affectionate cowherd boys and other inhabitants of Vṛndāvana immediately became stunned out of fear. They had dedicated everything to Kṛṣṇa: their lives, property, affection, activities—everything was for Kṛṣṇa—and when they saw Him in that condition, they became overwhelmed with fear and fell down on the ground. All the cows, bulls and small calves became overwhelmed with grief, and they began to look at Him with great anxiety. Out of fear they could only cry in agony and stand erect on the bank, unable to help their beloved Kṛṣṇa.
While this scene was taking place on the bank of the Yamunā, there were ill omens manifest. The earth trembled, meteors fell from the sky, and the left side of men's bodies shivered. All these are indications of great immediate danger. Observing the inauspicious signs, the cowherd men, including Mahārāja Nanda, became very anxious out of fear. At the same time they were informed that Kṛṣṇa had gone to the pasturing ground without His elder brother, Balarāma. As soon as Nanda and Yaśodā and the cowherd men heard this news, they became even more anxious. Out of their great affection for Kṛṣṇa, and being unaware of the extent of His potencies, they became overwhelmed with grief and anxiety because they had nothing dearer than Kṛṣṇa and because they had dedicated their everything—life, property, affection, mind and activities—to Kṛṣṇa. Because of their great attachment for Kṛṣṇa, they thought, "Today Kṛṣṇa is surely going to be vanquished!"
All the inhabitants of Vṛndāvana came out of the village to see Kṛṣṇa. The assembly consisted of children, old men, women, animals and all living entities; they knew that Kṛṣṇa was their only means of sustenance. While this was happening, Balarāma, who is the master of all knowledge, stood there simply smiling. He knew how powerful His younger brother was and that there was no cause for anxiety when Kṛṣṇa was fighting with an ordinary serpent of the material world. He did not, therefore, personally take any part in their sorrow. On the other hand, all the inhabitants of Vṛndāvana, being disturbed, began to search out Kṛṣṇa by following the impression of His footprints on the ground, and thus they moved hastily toward the bank of the Yamunā. Finally, by following the footprints marked with flag, bow and conchshell, the inhabitants of Vṛndāvana arrived at the riverbank and saw that all the cows and boys were weeping to behold Kṛṣṇa enwrapped in the coils of the black serpent. Then they became still more overwhelmed with grief. While Balarāma was smiling to see their lamentation, all the inhabitants of Vrajabhūmi merged into the ocean of grief because they thought that Kṛṣṇa was finished. Although the residents of Vṛndāvana did not know much about Kṛṣṇa, their love for Him was beyond comparison. As soon as they saw that Kṛṣṇa was in the river Yamunā enveloped by the serpent Kāliya and that all the boys and cows were lamenting, they simply began to think of Kṛṣṇa's friendship, His smiling face, His sweet words and His dealings with them. Thinking of all these and seeing that their Kṛṣṇa was now within the clutches of Kāliya, they at once felt that the three worlds had become vacant. Lord Caitanya also said that He was seeing the three worlds as vacant for want of Kṛṣṇa. This is the highest stage of Kṛṣṇa consciousness. Almost all of the inhabitants of Vṛndāvana had the highest ecstatic love for Kṛṣṇa.
When mother Yaśodā arrived, she wanted to enter the river Yamunā, and being checked, she fainted. Her friends, who were equally aggrieved, were shedding tears like torrents of rain or waves of the river, but in order to bring mother Yaśodā to consciousness, they began to speak loudly about the transcendental pastimes of Kṛṣṇa. Mother Yaśodā remained still, as if dead, because her consciousness was concentrated on the face of Kṛṣṇa. Nanda and all the other cowherd men, who had dedicated everything, including their lives, to Kṛṣṇa, were ready to enter the waters of the Yamunā, but Lord Balarāma checked them because He was in perfect knowledge that there was no danger.
For two hours Kṛṣṇa remained like an ordinary child gripped in the coils of Kāliya, but when He saw that all the inhabitants of Gokula—including His mother and father, the gopīs, the boys and the cows—were just on the point of death and that they had no shelter for salvation from imminent death, Kṛṣṇa immediately freed Himself. He began to expand His body, and when the serpent tried to hold Him, he felt a great strain. On account of the strain, his coils slackened, and he had no alternative but to let loose the Personality of Godhead, Kṛṣṇa, from his grasp. Kāliya then became very angry, and his great hoods expanded. He exhaled poisonous fumes from his nostrils, his eyes blazed like fire, and flames issued from his mouth. The great serpent remained still for some time, looking at Kṛṣṇa. Licking his lips with bifurcated tongues, the serpent looked at Kṛṣṇa with double hoods, and his eyesight was full of poison. Kṛṣṇa immediately pounced upon him, just as Garuḍa swoops upon a snake. Thus attacked, Kāliya looked for an opportunity to bite Him, but Kṛṣṇa moved around him. As Kṛṣṇa and Kāliya moved in a circle, the serpent gradually became fatigued, and his strength seemed to diminish considerably. Kṛṣṇa immediately pressed down the serpent's hoods and jumped up on them. The Lord's lotus feet became tinged with red from the rays of the jewels on the snake's hoods. Then He who is the original artist of all fine arts, such as dancing, began to dance upon the hoods of the serpent, although they were moving to and fro. Upon seeing this, the denizens of the upper planets showered flowers, beat drums, played different types of flutes and sang various prayers and songs. In this way, all the denizens of heaven, such as the Gandharvas, Siddhas and demigods, became very much pleased.
While Kṛṣṇa was dancing on his hoods, Kāliya tried to push Him down with some of his other hoods. Kāliya had about a hundred hoods, but Kṛṣṇa took control of them. He began to dash Kāliya with His lotus feet, and this was more than the serpent could bear. Gradually, Kāliya was reduced to struggling for his very life. He vomited all kinds of refuse and exhaled fire. While throwing up poisonous material from within, Kāliya became reduced in his sinful situation. Out of great anger, he began to struggle for existence and tried to raise one of his hoods to kill the Lord. The Lord immediately captured that hood and subdued it by kicking it and dancing on it. It actually appeared as if the Supreme Personality of Godhead Viṣṇu was being worshiped; the poisons emanating from the mouth of the serpent appeared to be like flower offerings. Kāliya then began to vomit blood instead of poison; he was completely fatigued. His whole body appeared to be broken by the kicks of the Lord. Within his mind, however, he finally began to understand that Kṛṣṇa is the Supreme Personality of Godhead, and he surrendered unto Him. He realized that Kṛṣṇa is the Supreme Lord, the master of everything.