The Nizhnyaya Tunguska (, meaning "Lower Tunguska") is a river in Siberia, Russia, that flows through the Irkutsk Oblast and the Krasnoyarsk Krai. The river is a right tributary of the Yenisey joining it at Turukhansk (see Siberian River Routes). Settlements on the river include Tura, Yukti and Simenga. The ice-free period on the Nizhnyaya Tunguska starts in mid-June and ends in the first half of October. The river forms the western limit of the Lena Plateau. Hydrography The Nizhnyaya Tunguska is the second largest right tributary of the Yenisey, and joins it near the town of Turukhansk. It is long, and has a drainage basin of . According to the character of the stream, constitution of the river's valley and its shores, it can be divided into two parts: the first one starts at the source of the river and continues down to the village Preobrazhenskoye and the second section of the river lies downstream of this village in a canyon-like relief. Upper stream The upper part of Nizhnyaya Tunguska is long and follows a wide valley with flat slopes that was formed by sand and clay deposits. The speed of flow at rafts reaches and drops significantly as the river's channel stretches. This section of river has a meandering channel that closely approaches the Lena, another great Siberian river. The minimum distance between them is as short as in the neighbourhood of Kirensk town. All of the upper course of Nizhnyaya Tunguska is within the Irkutsk Oblast. Lower stream Downstream of Preobrazhenskoye village the Lower Tunguska flows across the Tunguska Plateau of the Central Siberian Plateau in a narrow and deep valley with high, often rocky shores. The entire landscape here has volcanic origins, the relief alters the flow of Nizhnyaya Tunguska into a westerly direction. The river channel frequently has lake-like widenings with lengths up to and longer. The locations with close approaches of crystalline layers create numerous rapids on the river. The most significant of them have names such as: "Sakko", "Vivinskiy", "Uchamsky" and "Bolshoy" (, Big). The rapids on the river has relatively high speeds of water flux reaching . In some places downstream of the rapids the river channel becomes very deep with maximum depths of . In the river's lowest flow, downstream of join with its tributary river Severnaya, Nizhnyaya Tunguska runs between limestone rocks, which steeply rise from the water. The speeds