The Nymboida River rises in the northern foothills of the Barren Mountain, on the slopes of the Great Dividing Range, within Bellinger River National Park, west of Dorrigo.

Annual high rainfall on the Dorrigo Plateau produces strong river flows during most seasons.

[2] Flowing through Nymboi-Binderay National Park from Platypus Flat to The Junction confluence with the Little Nymboida River, there is a 27-kilometre (17 mi) section of rapid and pool sequences, making this a popular kayaking and white water rafting venue.

Located 13 kilometres (8.1 mi) from the source is Rob Roys Falls, a 90-metre (300 ft) cascade while further down river lies The Silent Pool, a geological mystery where the river goes underground via a fault line and returns under a large pool.

[citation needed] The river is also a stronghold for the endangered Eastern Freshwater cod where it is quite common in several reaches.