In Bukit Batu, there are small rivers turn into peat swamp, and some acidic lakes. Siak Kecil Wildlife Sanctuary includes in this area which consist of some small lakes but already degradated because of logging and over fishing.
Masked Finfoot (a female and a chick) observed on November 1992 in small mangrove in the coastal area (Burn & Brickle 1992). Local people reported that storks often visit the lake in Bukit Batu, probably Storm's Stork or Lesser Adjutant. Important bird species observed in this area all on October 1992 (Burn & Brickle 1992), but a small flock of White-winged Duck Cairina scutulata visits the lake in dry season.
Non-bird biodiversity: Crocodylus porosus and others crocodile species like Tomistoma schlegelii (Anon 1995). Elephant, tiger and tapir also live in this area (Scott 1989).
BirdLife International (2019) Important Bird Areas factsheet: Siak Kecil. Downloaded from http://www.birdlife.org on 23/03/2019.