City on the Irtysh (4)
I believe the answer is:
omsk
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">city on the irtysh</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for omsk that I've seen before include "City of south central Russia" , "Womble" , "Russian port" , "City in Siberia" , "Russian city" .)