The most common and most likely answer to this crossword clue is the 6 letter word FLOODS
F
L
O
O
D
S
Buddy explains!

The straight part
We know that "swamps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swamps = floods.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 FLOODS mean?
FLOODS noun- A (usually disastrous) overflow of water from a lake or other body of water due to excessive rainfall or other input of water.
- A large number or quantity of anything appearing more rapidly than can easily be dealt with.
- The flowing in of the tide, opposed to the ebb.
- A floodlight.
- Menstrual discharge; menses.
- Water as opposed to land.
- To overflow, as by water from excessive rainfall.
- To cover or partly fill as if by a flood.
- To provide (someone or something) with a larger number or quantity of something than can easily be dealt with.
- To paste numerous lines of text to (a chat system) in order to disrupt the conversation.
- To bleed profusely, as after childbirth.