Bihar is located in the eastern region of India between latitude 24°20'10"N– 27°31'15"N and longitude 83°19'50"E– 88°17'40"E. It is an entirely landlocked state, in a subtropical region of the temperate zone. Bihar lies between the humid West Bengal in the east and the sub humid Uttar Pradesh in the west, which provides it with a transitional position in respect of climate, economy, and culture. It is bounded by Nepal in the north and by Jharkhand in the south. Bihar plain is divided into two unequal halves (North Bihar & South Bihar) by the river Ganges which flows through the middle from west to east. Bihar's land has average elevation above sea level of 173 feet.
Bihar is in Indo–Gangetic plain, so naturally, fertile soil is one asset of the state. Thus, Indo–Gangetic plain's soil is the backbone of agricultural and industrial development. The Indo–Gangetic plain in Bihar consists of a thick alluvial mantle of drift origin overlying in most part, the Siwalik and older tertiary rocks. The soil is mainly little young loam rejuvenated every year by constant deposition of silt, clay, and sand brought by streams but mainly by floods in Bihar.
The soil is deficient in phosphoric acid, nitrogen, and humus but potash and lime are usually present in sufficient quantity. The common soil in Bihar is Gangetic alluvium of Indo–Gangetic plain region, Piedmont Swamp Soil which is found in northwestern part of West Champaran district and Terai Soil which is found in northern part of Bihar along the border of Nepal. Clay soil, Sand soil, and Loamy soil are common in Bihar
The state is divided into 9 divisions and has 38 districts. Begusarai followed by Katihar and Saharsa have the highest extent of wetlands about 10 % of the geographical area of the respective districts. The least extents (less than 1 percent) of wetlands has been in Kaimur (Bhabua), Nalanda, Sheikhpura, and Sitamarhi. The mean seasonal change in the extent of open water is about 37 % with Gaya district ranking first in terms of highest change (84 %) and Madhubani district showing the least change (5 %). In Supaul district has shown a slight increase in the extent of open water from post-monsoon (9004 ha) to pre-monsoon (9021 ha) which is due to non-seasonal rainfall. Aquatic vegetation variability is very high across the districts. It ranged from a minimum of about 2.5 ha (Rohtas district) to 3767 ha (Katihar district) in post-monsoon. While in pre-monsoon, wetlands in Rohtas district did not show the presence of aquatic vegetation but Vaishali registered a maximum extent (1884 ha). Kaimur district has shown aquatic vegetation of 6 ha, which remained unchanged in both the seasons. Overall, on an average each district has 681 ha in post-monsoon and 469 ha in pre-monsoon season. Analysis of data on turbidity reveals that Sheikhpura has least extent (17 ha) under low turbidity while Bhagalpur has the largest extent (12628 ha) in post-monsoon. The area statistics provided for each district has detailed tabular information on turbidity levels.
The aquatic vegetation in Bihar accounts for about 7 and 5 per cent of total wetland area in post-monsoon (25179 ha) and pre-monsoon (17360 ha) respectively.