Estuaries are semi-enclosed bodies of water usually at lower
reaches of rivers that have some connection to the open ocean and an input of fresh water that mixes with salt water
(OTA 1987).
By virtue of their proximity to the sea, estuaries are
areas subjected to 'salinity stress' which offer sheltered
habitat to essentially marine fauna which tolerate the lowered
and varying salinity regime in order to inhabit the food rich
muds. Two types of estuaries are recognised basin & riverine .
The summary of the current status of reasearch & management
issues are summarised by Samarakone 1987. Some work has been
done on variations of temperature salinity, pH, dissolved
oxygen rain fall in basin estuaries but little or no informa­tion exsists on pollution parameters and salt water intrusion
parameters of riverine estuaries. For this reason three river­
ine estuary systems Mahaoya, Kelani, Panadura-Bolgoda were
chosen for study based on proximity differing geography and in the case of the Kelani its importance as a major river.
(Fig. 1) An attempt was made to take into account tidal variations, both diurnal and monthly (spring & neap) which
could affect the various parameters studied.