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!”