[3] The national park is situated along the Mahaweli flood plain and is considered a rich feeding ground for elephants.

The rich alluvial soil flood plains situated beside the river are featured by a number of shallow swampy depressions called "villus".

[5] The villus system of Mahaweli River has received protected status from Flood Plains and Somawathiya National Parks.

[6] The extended inundation of these low-lying areas, along with the nutrients carried in by the water, are the cause of the high level of net primary productivity.

Relative humidity range from 60 to 90% depending on the rainfall patterns and the area experience strong seasonal windy periods.

On the right bank of the river, at the edge of the Mutugalla villu, ruins of an ancient cave monastery with inscriptions dating back to between 2nd and 7th century BC have been found.

There are 231 plant species that have recorded from Handapan and Bendiya villus and marsh forests, which is the largest villu of 796 hectares (3.07 sq mi) within the Mahaweli River floodplain.

[3] The vegetation of the villus shows distinct pattern of zonation with creeping grasses such as Cynodon dactylon, and essentially terrestrial annual plants on the edges.

[3] The rich vegetation in the villus attract large numbers of herbivores and aves and supports a higher annual biomass than any other form of habitat within the accelerated Mahaweli development project area.

Common residents are eastern large egret Egreta alba, cattle egret Bubulcus ibis, Painted stork Ibis leucocephala, pond heron Ardeola grayii, eastern grey heron Ardea cinerea, pheasant-tailed jacana Hydrophasianus chirurgus, purple coot Porphyrio porphyrio, Indian darter Anhinga rufa, little cormorant Phalacrocorax niger, Indian shag P. fuscicollis, Indian cormorant P. carbo sinensis, brahminy kite Haliastur indus, painted snipe Rostratula benghalensis, black-winged stilt Himantopus himantopus, and red-wattled lapwing Vanellus indicus.

[3] Together with adjoining Somawathiya National Park, Flood Plains provides a sanctuary for a wide variety of resident and migratory waterfowls.

The construction of dam on the Mahaweli River will inevitably drop water flow and thereby reduce the magnitude and duration of flooding downstream.