The most common and most likely answer to this crossword clue is the 6 letter word SWAMPS
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More clues leading to the result SWAMPS
Buddy explains!

The straight part
We know that "wetlands" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wetlands = swamps.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SWAMPS mean?
SWAMPS noun- A piece of wet, spongy land; low ground saturated with water; soft, wet ground which may have a growth of certain kinds of trees, but is unfit for agricultural or pastoral purposes.
- A type of wetland that stretches for vast distances, and is home to many creatures which have adapted specifically to that environment.
- A place or situation that is foul or where progress is difficult.
- To drench or fill with water.
- To overwhelm; to make too busy, or overrun the capacity of.
- To plunge into difficulties and perils; to overwhelm; to ruin; to wreck.