Pakistan has significant natural resources including crude oil, natural gas, coal, water, land, uranium, and minerals. Coal resources make up a large portion of Pakistan's energy supply but many coalfields remain underdeveloped. Water resources are mainly derived from the Indus River and its tributaries but surface water is often wasted through flooding. Land resources support agriculture as the most important crops are cotton, wheat, rice, and sugarcane. Uranium and various minerals like chromites, copper, and gypsum are located throughout Pakistan but the mineral sector currently only contributes 0.5% to GDP.