The Mahakam, one of Indonesia’s mightiest rivers, is home to endangered freshwater dolphins in Kalimantan. Conservation group Rare Aquatic Species of Indonesia (RASI) estimates their number at 80. Pollution from the mining industry and logging has been largely blamed for their endangerment. The Jakarta Post correspondent in Balikpapan, East Kalimantan, Nurni Sulaiman, recently joined researchers and activists on a three-week trip along the Mahakam River to monitor the animals’ degrading habitat and conservation efforts.

by Nurni Sulaiman

Sailing upstream from the provincial capital of Samarinda to Kutai Kartanegara, some 75 kilometers to the northwest, we passed countless vessels of all sorts. In Kalimantan, a vast but sparsely populated island, rivers are just like busy highways in the more developed Java. In downstream areas closer to the estuary, staggering coal-laden bulk carriers looked like clusters of floating hills from...