Rivers and Lakes. Water covers 2,112.54 hectare of the total area of Darkhan-Uul aimag and from this, rivers take up 1,998.0 hectare, lakes take up 24.0 hectare and industrial water funds take up the remaining 1.0 hectare. Rivers such as Zulzaga river, Sharyn Gol river, Yeruu river, Orkhon river, Khuitnii river and Khavchuun river that are originated from the Khangai Mountains and flow to join the Orkhon River belong to this aimag.
Fauna. Various kinds of animals inhabit the territory of Darkhan-Uul aimag such as bear, deer, fox, corsac, wolf, lynx, boar, musk deer, roe deer, rabbit, squirrel, and badger. There are 12 species of water birds such as swan and scoter also 14 species of birds such as bobwhite, magpie and cap reside in Darkhan-Uul province. Also, 8 different species of fish such as taimen, lenok, dog-fish and jackfish inhabit in the river and lakes of the aimag. The taimen (Hucho taimen), also known as Siberian taimen, is a species of fish in the salmon family (family Salmonidae). According to Mongolian legend, giant taimen trapped in river ice. Local herders were able to survive the winter by hacking off pieces of its flesh. In the spring, the ice melted and the giant taimen climbed onto the land, tracked down the herders, and ate them all.