Usta(redirected from USTO)
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a river in Gorky and Kirov oblasts, RSFSR; a left tributary of the Vetluga River of the Volga River basin. The Usta is 253 km long and drains an area of 6,030 sq km. It is fed mainly by snow. The mean flow rate 47 km from the mouth is 28 cu m per sec. The river freezes over in November, and the ice breaks up in April. The Usta is used to float timber. The river is navigable in its lower course.