Öskemen (ösˈkĭmĭnˌ) [key], formerly Ust-Kamenogorsk ŏstˌ-kəmyĭnəgôrskˈ, city (1989 pop. 324,478), NE Kazakhstan, on the Irtysh River and in the foothills of the W Altai Mts. It is a river port and an industrial center with zinc, lead, and titanium-magnesium smelters. There is a large hydroelectric station nearby. The city was founded in 1720 as the Russian military outpost of Ust-Kamennaya.