The journey begins at the port town of Kumai, where klotok and speedboats gather to take you the short distance across to the mouth of Sungai Sekonyer. It is largely muddy due to upstream mining operations, although it eventually forks into a naturally tea-coloured tributary, typical of peat-swamp waterways. The upriver journey contains several noteworthy stops – you won't necessarily see everything, nor will it be in this order.
Tanjung Harapan Orang-utan feeding station with refurbished interpretation centre; feedings at 3pm daily.
Sekonyer Village A small village that arose around Tanjung Harapan, but has since been relocated across the river, where most residents work in the palm-oil industry. There are a couple of lodgings here.
Pasalat A reforestation camp where Pak Ledan plants saplings and maintains the medicinal plant garden.
Pondok Tanggui Orang-utan feeding station; feedings at 9am daily.
Pondok Ambung Research station, popular for spotting tarantulas and glowing mushrooms on ranger-guided night hikes.
Camp Leakey The final stop. The original and still-active research station with an informative visitor centre. Feedings occur at 2pm daily at a platform a 30-minute walk from the visitor centre.
Klotok call at three stations where rangers stack piles of bananas and buckets of soy milk to feed the resident population of ex-captive and semi-wild orang-utans. There are no fences or cages, but you'll be kept at a distance by ropes – a boundary ignored by the animals themselves, which often wander nonchalantly through the shutter-snapping crowd on their way to lunch. While some orang-utans appear deceptively tame, do not attempt to touch or feed them, and do not get between a mother and child. Orang-utans are several times more powerful than you, and may bite if provoked.
Apart from the orang-utan feeding stations, there's plenty of opportunity for wildlife spotting from the boat. Watch for the quick flash of the colourful kingfisher, and scan the shallows for the toothy false gharail or saltwater crocs – the presence of crocodiles means swimming the river is out of the question. In the evening you can spot proboscis monkeys bedding down in the treetops with the river at their backs for protection. These curious golden-haired, round-bellied, bulbous-nosed primates are found only on Borneo and are sometimes called monyet belanda (Dutch monkey). At night you tie up on the river, set mattresses and mosquito nets on deck, and drift off to the hum of the rainforest.