Nepal is the second largest country after Brazil in water resources. There are thousands of rivers in the country. Most of the big rivers originate from the mountain and middle hill. The ricers originating from the mountain such as arun , tamakoshi , kaligandaki , karnali and so on, are snow fed rivers . these are perennial rivers .the flow water in the river originating from the middle hill decreases during winter .the rivers originating from the churiya are non-perennial so that sry up in the winter season .

There are three most important rivers systems in Nepal such as koshi ,gandaki and karnali , koshi is the longest rives of Nepal .it has sevefn tributaries namely arun sunkoshi , tamakoshi ,likhu ,dudhkoshi , indrawati and tanro that drain the eastern region of the country .

Gandaki flows in the central part of the central part of the country. it has secen main tributaries namely kali-gandaki marsyangdi , trusuli ,seti , madi and daraudi  , similary , karnali  flows in the western part of the country . its main tributaries are humal karnali , magu karmali ,bheri , tila ,and seti besides these main rivers , there are many important rivers of second and third order some of them are  mechi , kankai ,kamala, bagmati ,ratu , lai bakaiya , bakaiya mabana , tinau rapti , babai ,mahakali and so on .