Tidal Wetland on the Coast, With Mucky Deposits
Puzzle 13 of Flat Things Easy Pack
Question is: Tidal Wetland on the Coast, With Mucky Deposits
and the answer is: MUDFLAT
Word Meaning:
MUDFLAT — A muddy expanse of flat land, especially such land as a riverbed exposed at low tide.
Definitions from Wiktionary.