Dudh Koshi

The Dudh Koshi — the 'milk river', named for its glacial-white water — is Everest's river. It rises east of the Gokyo Lakes at about 5,100 m and collects the meltwater of the whole Khumbu: the Bhote Koshi coming down from the Nangpa La side and the Imja Khola from the Imja valley below Everest and Lhotse. Every trekker bound for Everest Base Camp walks its gorge, crossing and re-crossing the river on the high suspension bridges below Namche Bazaar.

Its upper catchment is enclosed by Sagarmatha National Park (1,148 km²), Nepal's first natural World Heritage Site, inscribed by UNESCO in 1979. The basin has become a natural laboratory for Himalayan glacier science: modelling published in The Cryosphere (Shea et al. 2015) put the Dudh Koshi basin's ice loss between 1961 and 2007 at ≈6.4 km³ of glacier volume (about 15.6%) and ≈101 km² of glacier area, with far larger losses projected over this century — a long-term concern for the river's dry-season flow.

The Dudh Koshi is also some of the steepest navigable whitewater on Earth, with rapids to class VI that have drawn expedition kayakers descending from Everest itself. Its high, steady glacier-fed flow makes the basin a leading candidate for storage hydropower — including the long-studied Dudh Koshi reservoir scheme — alongside operating run-of-river plants on the Solu Khola tributary. The river finally joins the Sun Koshi at Harkapur, at just 1,245 m, almost four vertical kilometres below its source.