Which one of the following is not a lagoon?

Ashtamudi, Chilka and Pulicat are cited in standard geographic sources as coastal lagoons formed by sandbars and spits: Ashtamudi (Asthamudi), Chilka and Pulicat appear together in lists of Indian lagoons [1]. Texts describing India’s coastal features also identify Chilka and Pulicat as important lagoons on the eastern coast, reinforcing their classification as coastal lagoons [2]. In contrast, “Preiyar” (Periyar) refers to a freshwater inland waterbody associated with the Periyar River and the Thekkady/Periyar reservoir in the Western Ghats; it is not a coastal lagoon formed by barrier bars and sea enclosure, so it is the odd one out.

Sources

1. [1] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > 7. Lagoons > p. 28
2. [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 2: Physiography > The Eastern Coastal Plain > p. 66