Air Terjun Nokan Nayan, 180-meter waterfall in Ambalau District, Sintang, Indonesia.

Air Terjun Nokan Nayan is a waterfall in Deme village, Ambalau district, Sintang regency, West Kalimantan, over 180 metres high and among the tallest in Indonesia. It is actually two falls: Nokan Nayan, formed by the Lonayan river, and Jongonoi, formed by the Jongonoi river, which drops beside it from almost the same height at the head of a valley. Both sit at about 200 metres above sea level.

The waterfall lies in Deme village, Ambalau district, Sintang regency, West Kalimantan, at about 200 metres above sea level. It is formed by two rivers, the Lonayan and the Jongonoi, which drop at the same point at the end of a valley; the Jongonoi fall, Air Terjun Jongonoi, sits directly beside the main fall and is nearly the same height. In 2019 the Sintang regency government targeted operation of a 2x50 MW hydroelectric plant using the Nokan Nayan and Nokan Jengonoi falls.

The Ot Danum name Nohkan Lonanyan combines nohkan, meaning waterfall, with Lonayan, the river that forms it. Residents regard the site as a village of spirits and hold certain customary rituals there, so several prohibitions must be observed; visitors ask the village head and adat leader for permission and for guides.

Visitors should prepare for difficult terrain and wet conditions, as the area remains natural and slippery underfoot. Arranging a local guide and checking with village authorities before arriving is strongly advised.

The two falls drop at the same spot at the end of a valley: Nokan Nayan from the Lonayan river and Jongonoi from the Jongonoi river, both at about 200 m above sea level. In the rainy season the large discharge throws up high mist and forms a permanent rainbow below at midday.