Barguzin (Russian: Баргузин; Buryat: Баргажан Bargažan) is a river in Buryatia, Russia of length 480 km flowing into the Barguzin Bay of Lake Baikal, the largest and deepest bay of Baikal. Barguzin is the third (by the flow amount) inflow of Baikal, after Selenga and Upper Angara River. Its watershed area is 21,100 km². It is navigable for 204 km upwards from its estuary. Its main tributaries are the Gagra, Argada, Ina and Ulyun rivers. In 1648 Ivan Galkin founded an ostrog on the Barguzin.
In its middle part Barguzin river flows along the Barguzin Valley (Barguzin Depression, Russian: Баргузинская котловина), which is 200 km long of width up to 35 km and runs between the Barguzin Range (to the North-West) and Ikat Range (to the South-East). In the valley the river branches, loops, leaves old river-beds and creates a swampy water network with more than 1000 lakes. In the valley there is Dzherga State Nature Preserve (Russian: Джергинский государственный природный заповедник) of area 2,387 km².
The river also gave its name to a steady, strong North-Western Barguzin wind on Baikal. The air flow rushes unto Baikal from the Barguzin Valley and blows across the lake at its middle. Usually Barguzin blows no longer than day and night, but mostly it starts at the sunrise and ends by the sunset. Usually it brings sunny weather. In Barguzin Bay it may be of hurricane strength, but average speed is usually less than 20 m/s. The wind is commemorated in the Russian folk song about a runaway from the Akatuy katorga: