Kayamkulam Kayal, Kayamkulam Lake or Kayamkulam Estuary is a shallow brackish water lagoon streaching between Panmana and Karthikapally. It has an outlet to the Arabian sea at Kayamkulam barrage. The Kayal used to be connected to the sea most of the time except during dry season when a bar like formation separates it from the sea. Now the bar has been opened up permanently for construction of Kayamkulam Fishing Harbor. Kayamkulam boat race is conducted in Kayamkulam Kayal.
There is a popular belief that Kayamkulam kayal was once lush green fields and Kayamkulam Raja, angry and desolate from being defeated by Travancore King Marthanda Varma, ordered his naval officers, Arattupuzha Arayars, to rupture the barrier separating it from the sea and let salt water in to make the fields un-cultivable. It is believed that when Kayamkulam was annexed the King threw all the valuables in his palace into Kayamkulam lake and fled the Kingdom.
In Aithihyamala it is mentioned that Kayamkulam Kochunni sunk his mother-in-law, after killing her, in Kayamkulam Lake.