The most common and most likely answer to this crossword clue is the 7 letter word AQUATIC
I've seen this crossword clue in Independent
A
Q
U
A
T
I
C
More clues leading to the result AQUATIC
- A quantity of liquid runs out, I see, like water?
- Like swimming from a short wharf? That’s correct, mostly
- Like a duck it rises, cutting a duck’s cry short
- A queen has short moment as a fish?
- Acquit a drunk, now living on water
- A qualified university algologist tended only the tips attached to one cold water plant
- Living on water, heavy drinkershave the odd twitch!
- A question on a mark left incomplete and relating to water
- “All wet,” as in “a jerk”
Buddy explains!

The straight part
We know that "Like a duck" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like a duck = aquatic.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 AQUATIC mean?
AQUATIC noun- Any aquatic plant.
- Relating to water; living in or near water, taking place in water.