Olenyok – the river flows mainly in the Republic of Sakha (the upper course is in the Krasnoyarsk Region). The length is 2,292 km; the basin area is approx. 220,000 km2. It flows into the Gulf of Olenyok of the Laptev Sea, forming a delta (the area of 475 km2). It is cataracted. The flow is 40 km3/year. The average water runoff is 1,210 m3/s. It contains ice formations from the end of September–October to late May–early June. It is navigable in the lower reaches. It is rich in fish (whitefish, cisco, white salmon, etc.).