The Bario area also forms the headwaters of Limbang, Kuba-an, Libun, and Dapur rivers; the latter two are the important tributaries for the Tutoh and Ulu Baram rivers. A survey done in 1995 found that the pH of river waters around Bario was acidic, ranging between 4.8 and 5.2. This can be explained by the leaching of acidic organic materials from soil into water. Water stream draining the Bario Asal area was of good quality with a high level of dissolved oxygen and a low amount of suspended solids. However, to the east of Bario Asal, water was of poorer quality due to deforestation and agricultural activities. Pollution from chemicals was insignificant due to low usage of chemical fertilisers.