Surface of estuary leading to pool (6)
I believe the answer is:
emerge
'surface' is the definition.
(emerging is a kind of surfacing)
'estuary leading to pool' is the wordplay.
'leading' indicates taking the first letters.
'to pool' becomes 'merge' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'estuary' is 'e'.
'e'+'merge'='EMERGE'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for emerge that I've seen before include "Issue" , "Come into view" , "Become gradually apparent" , "Come forth or appear" , "Emanate" .)