Cryptic crossword clue
Contaminate fin, etc, when swimming 6

The most common and most likely answer to this crossword clue is the 6 letter word INFECT

I
N
F
E
C
T

Buddy explains!

The straight part
We know that "Contaminate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case contaminate = infect.
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 INFECT mean?

INFECT verb
  1. To bring into contact with a substance that causes illness (a pathogen).
  2. To make somebody enthusiastic about one's own passion.
INFECT adjective
  1. Infected.

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