Udai River [Udaj]. (Map: Udai River.) A right-bank tributary of the Sula River that flows for 327 km through Chernihiv oblast and Poltava oblast and drains a basin area of 7,030 sq km. The river is 5–10 m wide in its upper reaches and 20–40 m wide along its lower course. Wetlands are found in several sections of its basin. The river is used for industry, water supply, and fishing. The cities of Pryluky and Pyriatyn are situated along it.

[This article originally appeared in the Encyclopedia of Ukraine, vol. 5 (1993).]