The Udai finds its source near the village of Rozhnivka in Pryluky Raion, Chernihiv Oblast. The river flows through the Dnieper Lowland, within the Chernihiv Oblast and the Poltava Oblast. It is predominantly fed by melting snow (nival regime). It freezes between November and early January, and it stays under the ice until March to mid April.[2] The average discharge of the Uday at 39 km from the mouth is 9.4 m3/s (330 cu ft/s).[2]
The towns of Pryluky and Pyriatyn lie on the Udai,[2] as well as the urban-type settlements of Dihtiari, Varva, Ladan, and the village(selo) of Pisky-Udajsjki.
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Hydrochemistry of the rivers of the Left Bank forest-steppe / Ed. VK Khilchevsky, VA Stashuk. - K .: Nika-Center, 2014. - 230 p. ISBN978-966-521-107-5
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