The most common and most likely answer to this crossword clue is the 5 letter word GATOR
I've seen this crossword clue in Financial Times
G
A
T
O
R
More clues leading to the result GATOR
- Gold piece comes first for Florida resident, say
- Snapper dropping camera went to mender, finally
- It lurks in the everglades from Georgia to heart of Florida
- Partly reviving a torpid swimmer
- Toothy beast jumping at oranges — only some taken
- Predator almost devoured drenched in endless blood
- Snapper with good roll used up
- Reptile found by girl on a mountain
- Reptile skips the end of the door and takes another gate
- Georgia Hill is a Florida jock
Buddy explains!

The straight part
We know that "swimmer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swimmer = gator.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 GATOR mean?
GATOR noun- Alligator.