Aquatic Ecosystems

 

Rivers

The country is endowed with tremendous inland water resources. There are extensive network of rivers, rivulets and streams arising from high level of precipitation, presence of huge number of glaciers and glacial lakes, and relatively well-preserved forests. The country’s river system can be divided into four major river basins, namely Amo Chhu (Torsa), Wang Chhu, Puna Tsang Chhu (Sunkosh), and Drangme Chhu (Manas). Drangme Chhu, which is the largest river basin, drains more than one-third of the country. In addition, there are several small river basins occupying largely the southern part of the country. These include Samtse Area multi-river, Gelegphu Area multi-river, Samdrup Jongkhar Area multi-river, and Shingkhar-Lauri multi-river.

Lakes

There are a large number of small and medium-sized lakes spread across the country. At present, except for glacial lakes, there is no adequate assessment of the area and location of various lakes in the country. As for glacial lakes, the inventory of Glaciers, Glacial Lakes and Glacial Lake Outburst Floods in Bhutan produced in 2001 by the Department of Geology and Mines reports a total of 2,674 lakes in the country. However, most of the glacial lakes are extremely small. The largest of all the lakes is the Raphstreng Tsho at an altitude of 4,360 m in the north-west part of Bhutan.

Marshlands

In addition to rivers and lakes, marshlands in the form of depressions and water-logged areas, are envisaged to be a major part of the aquatic ecosystems in the country although no proper survey of marshlands have been carried out so far. Marshlands are generally known to be rich in biota and good habitat for resident as well as migratory birds, reptiles, amphibians and fishes. The best known marshland in the country is the Phobjikha valley, where the globally threatened black-necked cranes Grus nigrocollis roost in large numbers during winter..