hradah kascid visagnina
patanty upari-gah khagah
Sri Sukadeva Gosvami said: Within the river Kalindi [Yamuna] was a lake inhabited by the serpent Kaliya, whose fiery poison constantly heated and boiled its waters. Indeed, the vapors thus created were so poisonous that birds flying over the contaminated lake would fall down into it.
In this regard the acaryas explain that the Kaliya lake was situated apart from the main current of the river; otherwise the Yamuna’s waters would have been poisonous even in cities like Mathura and in other places farther away.