The western edge of Eastern Russia has the eastern edge of the the West(1)-Siberian Lowland(2), more or less west of the Yenisey(3) River. This very flat land is poorly drained, often marshy, and some river flood plains are tens of kilometers wide. The Yenisey itself forms a wide delta with many distributaries that ends in a long inlet or bay (zaliv). Farther south, where Eastern Russia extends westward, far more of this flatland is included, and in these latitudes it is drier. Here is the upper course of the Ob'(4).
(1) Zapadno in transliterated Russian.
(2) Nizmenmost' in transliterated Russian.
(3) Also transliterated from Russian as Jenesej. The Yenisey-Angara combination is the world's fifth longest and Asia's second longest.
(4) The Ob'-Irtysh combination is the world's fifth longest and Asia's second longest.