Brunei is located in the northwestern coast of the island of Borneo. It covers a land area of 5,765 kilometers. Its nearest neighbor is Sarawak, the eastern state of Malaysia. The districts of Brunei-Muara, Tutong and Belait make up the larger western portion and are dominated by hilly lowlands, swampy plains and valleys. The eastern district of Temburong is more mountainous and has a land area of 1,288 sq. kilometers.

There are 4 main rivers that channel into the 4 districts of Temburong, Belait, Tutong and Brunei. The smallest river of all is the Temburong. It drains nearly the whole district.

Two other main rivers are the Belait and Tutong. The Belait basin is the largest with a total area of 2,700 sq. kilometers. The Tutong basin is about 1,300 sq. kilometers.