the name black irtysh ("kara-irtysh" in kazakh, or "cherny irtysh" in russian) is applied by some authors, especially in russia and kazakhstan, to the upper course of the river, from its source entering lake zaysan. the term white irtysh, in opposition to the black irtysh, was occasionally used in the past to refer to the irtysh below lake zaysan; now this usage is largely obsolete.