a river in the Yakut ASSR with its upper reaches in Krasnoiarsk Krai, RSFSR. It is 2,292 km long and drains an area of 220,000 sq km.

Originating in a small lake on the northern edge of the Viliui Plateau, the Olenek flows east along the Bukochan Ridge, and then through a narrow valley and, in places, northward through a canyon. Of the Olenek’s white-water stretches, the Ukoian Rapids are particularly difficult to navigate. The middle Olenek, below the mouth of the left tributary Arga-Sala, meanders through a wide valley. Here the largest tributaries are the Siligir River on the right and the Unukit, Birekte, Kuoika, and Been-chime rivers on the left. The lower Olenek dissects the Kystyk Plateau. After the influx of the Bur River from the left, the Olenek flows northwestward along the Chekanovskii Ridge through the Northern Siberian Lowland. Emptying into the Olenek Gulf of the Laptev Sea, it forms (below Cape Tumulo) a delta approximately 20 km long with an area of 475 sq km.

The main arms are the Ulakhan-Uesia on the left and the Kubala-Uesia. The major left tributaries are the Bur and Buolk-alakh. The Olenek is fed by snow and rain. High water occurs from June through September; low water, from October through May. The mean flow rate at the mouth is 1,210 cu m per sec; when the river is frozen, the flow rate of the lower course may be less than 1 cu m per sec. Some years the Olenek freezes down to the bottom and remains thus for a month. The upper course is completely frozen (to the bottom) from January until April. The river freezes in late September or October; breakup occurs in late May or the first half of June. Rich in fish, the Olenek has least cisco, arctic cisco, muksun (Coregonus maksun), nelma (Stenodus leucichthys nelma’), and taimen (Hucho taimen). Situated on the river are the settlements of Olenek, Taimylyr, and Ust’-Olenek.