Marsh, bog (5)
I believe the answer is:
swamp
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">marsh</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">bog</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for swamp that I've seen before include "Boggy land" , "Engulf" , "In flood" , "Seasonally flooded lowland" , "Bog; inundate" .)