Wikipedia
Chakara (also spelt Chaakara & ചാകര) is a Malayalam word used to describe a peculiar marine phenomenon in which a large number of fish and prawns throng together during a particular season as a result of mud bank formations. It is derived from Sanskrit Chakra which has similar meanings. This rare phenomenon is observed only along the coastal waters of the Indian state of Kerala, especially around the coast of Purakkad and in South America, where it has proved to be a boon for the local fisherfolk.
A correct scientific explanation about the formation of a chakara is debatable. However, a strongly supported theory is that during the monsoons, the water level of the backwaters rises which facilitates the movement of fine clay particles into the sea through the subterranean channels. The accumulation of organic material by this process in relatively calm regions of the sea during the monsoons attracts fish.
This phenomenon is demonstrated in Chemmeen. It is greeted, celebrated, and described in the song "Puththan Valakkare."