The Fox River (originally the Potikohua River^[1]) is a river in the Buller District of New Zealand. It arises in the Paparoa Range near Mount Dewar and flows north-west through the Paparoa National Park to the Tasman Sea at Woodpecker Bay.^[2] The river passes through a spectacular gorge. The northern branch of the river has limestone caves containing stalactite and stalagmite formations.

The river was named after Bill Fox, a gold prospector.^[3] The Māori name Potikohua, comes from poti, a cooking basket, and kohua, steaming oven.^[4]

The Fox River has its origins high in the Paparoa Range, and flows in a north-west direction through the limestone syncline. The river passes through deep limestone canyons on its way to the coast.^[5] One of the main tributaries is Dilemma Creek.

The river valley is characterised by limestone escarpments, with steep sloping faces beneath. The forest type on these slopes is variable in height and composition. Common species include the nīkau palm (Rhopalostylis sapida), and tree ferns (especially mamaku (Sphaeropteris medullaris), pigeonwood (Hedycarya arborea), māhoe (Melicytus ramiflorus), kamahi (Weinmannia racemosa), and hīnau (Elaeocarpus dentatus), but nīkau and mamaku are often the most common. Above the steep slopes there are some large northern rata (Metrosideros robusta) and rimu (Dacrydium cupressinum), with occasional miro (Prumnopitys ferruginea). Rimu and miro are mainly present on the more gentle slopes, while northern rata is the only emergent tree on the steeper slopes below escarpments.^[5]