A dense tan flow of sediments makes its way into the South China Sea from the mouth of the Rajang River in Sarawak, Malaysia. The river is located in northwest of Borneo and it originates in the Iran Mountains. The river flows approximately 563 km to the sea, making it the longest river in Malaysia.
Up the coast, sediments can also be seen on the northern shores of Brunei Bay, the gateway to Brunei and Borneo. It is located east of Bandar Seri Begawan. It is a deeply indented bay with an area of about 250,000 ha, shared between Brunei Darussalam and the East Malaysian States of Sarawak and Sabah.
A chain of islands including the large Malaysian island of Labuan forms the boundary between the bay and the South China Sea. Freshwater flows into the bay via a labyrinth of interconnecting channels and waterways.
Most of the east and south shores of the bay are covered in extensive mangrove forests with associated mudflats and sandflats at the mouths of the major estuaries. The mangrove forests form a continuous, intact forest within Bruneian territory, but those within the adjacent Sarawak territory have been largely clear-felled to supply the wood-chip industry.
The major rivers entering the Brunei Estuary in the southwest are the Brunei, Limbang, Temburong, Bangar and Trusan. The Limbang and Temburong drain catchments which are predominantly primary rainforest, and carry high silt loads.
The smaller Brunei River receives the drainage from the city of Bandar Seri Begawan and its environment, and is therefore subject to considerable urban pollution. Several smaller rivers drain the extensive peat swamp forests of Temburong District. These carry very small silt loads, but are rich in peat and woody debris.