The most common and most likely answer to this crossword clue is the 10 letter word RESURFACED
I've seen this crossword clue in The Daily Telegraph
R
E
S
U
R
F
A
C
E
D
Buddy explains!

The straight part
We know that "emerged from water again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case emerged from water again = resurfaced.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 RESURFACED mean?
RESURFACED verb- To come once again to the surface
- To provide a new surface, to replace or remodel the surface of something, or to restore a surface. To put a new coating or finish on a surface.
- To arise or become evident again. To re-occur or reappear.
- To make something reappear.
- (of a person) To come out of hiding or obscurity.