The most common and most likely answer to this crossword clue is the 9 letter word LONGSHORE
I've seen this crossword clue in Independent
L
O
N
G
S
H
O
R
E
Buddy explains!

The straight part
We know that "very close to sea" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case very close to sea = longshore.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.
Crossword Answer definitions
LONGSHORE adjective- Of, relating to, or living along a seacoast.
- (of a current) Flowing parallel to the shoreline, or diagonal to it, rather than perpendicular to it.