Ramp alongside water, edge cut into rock (7)
I believe the answer is:
slipway
'ramp alongside water' is the definition.
'edge cut into rock' is the wordplay.
'edge' becomes 'lip' (lip is a kind of edge).
'cut into' indicates putting letters inside.
'rock' becomes 'sway' (synonyms).
'lip' going into 'sway' is 'SLIPWAY'.
(Other definitions for slipway that I've seen before include "where vessels are launched" , "Launching place" , "Launch ramp" , "Launch slope for ships" .)