Malaysia has a high rainfall rate. In February 2012, the total
rainfalls were between 175% and 485% above average in the
northern area, and between 66% and 122% above the monthly
average on the west coast of the Peninsula Malaysia [56]. The
average rainfall throughout the whole country is approximately
250 cm per year [57]. The main rivers in the west of the
Peninsular of Malaysia, such as: Sungai Perak (390 km), Sungai
Selangor (80 km), and Sungai Muar (190 km) are drained into the
Straits of Malacca (main river) [58]. Exchange of organic matter and mineral nutrients occur in the estuary area and hence, a
salinity gradient is generated [59]