Great ledges partly receding in river estuary (5)
I believe the answer is:
delta
'river estuary' is the definition.
'delta' can be an answer for 'estuary' (I've seen this in another clue). I'm not sure about the 'river' bit.
'great ledges partly receding' is the wordplay.
'partly' indicates the answer is hidden within the clue (part of the clue is used).
'receding' says the letters should be written backwards.
'atled' can be found hidden inside 'great ledges'.
'atled' back-to-front is 'DELTA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for delta that I've seen before include "Comms code for 'd'" , "Multiple estuary" , "Fragmented estuary" , "one's often seen at mouth of river" , "Extended area at river mouth" .)