Hydrology is generally a scientific study on water. Water plays enormous roles in the physical environment. International Scientific Hydrology Association has acknowledged four main disciplines in hydrology: surface water, groundwater, snow and ice, and limnology—pond study. Malaysia is divided into two distinct parts: Peninsular Malaysia at the southern tip of continental Asia and the states of Sarawak and Sabah at the northern part of Borneo Island. The amount of rainfall received in both Peninsular Malaysia and the states of Sarawak and Sabah is mainly influenced by seasonal variation known as the southwest and northeast monsoons. The drainage system in Peninsular Malaysia has evolved since the land emergence and is likely to have been established at the time of maximum marine transgression in the Middle Miocene. Lakes in Malaysia are natural and artificial in origin. Natural lakes are not common in this country due to the lack of internal drainage pattern.