The most common and most likely answer to this crossword clue is the 6 letter word INLETS
I've seen this crossword clue in Independent
I
N
L
E
T
S
More clues leading to the result INLETS
Buddy explains!

The straight part
We know that "coastal features" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coastal features = inlets.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 INLETS mean?
INLETS noun- A body of water let into a coast, such as a bay, cove, fjord or estuary.
- A passage that leads into a cavity.