Abstract
Field investigations were conducted on 22 November 2011during rainy season and 16 March 2012 during dry season to estimate the present state of density stratification of Koggala Lagoon, Sri Lanka. The variation of salinity, water temperature and dissolved oxygen were measured vertically at the neap tide condition. Koggala lagoon exhibits an entirely different mixing state depending on the season. In rainy season, lagoon water was brackish and in weak mixing state. On the other hand, in dry season, water in both the lagoon mouth and inside the lagoon exhibit the state of strong mixing and high salinity. In both seasons, high temperature, high salinity and, low dissolved oxygen at the deep layer of water were found in the central part of the lagoon. The salinity level at the bottom was higher than the estimated level based on water budget analysis.
