Tasek Merimbun In Brunei Darussalam is the important lake. The unique black water lake known as Tasek Merimbun is the largest lake in Brunei. Two rivers, Sungai Meluncur and Sungai Bang Oncom, flow into the lake. The waters from the two rivers are almost black because they flow through swamp forests full of peat on their way to the lake. Tasek Merimbun naturally has an unusual S-shape. There is a small island in the center, which is accessible by way of a timber walkway.