Negombo estuary is one of the most productive estuaries in Sri Lanka. It is 12 km in length from south to north and 3.75 km at its widest point. The mean depth of the estuary is about 1.2 m. The greatest recorded water depth is 2.6 m but 10% of the estuary has a water depth of less than 0.5 m (Figure 01). The estuary covers an area of approximately 35 km2 and opens to the sea at its northern end. To the south, it is connected to the Muthurajawela marsh which covers an area of approximately 31 km2 and together the estuary and marsh constitute a conjoined, tidally influenced coastal wetland. The main fresh water input comes from the rivers Dandugam Oya and Ja-ela but the lagoon is characterized by a brackish water flora and some mangrove forests in the northern part.