Estuary flowing around river presumably holds a number of deposits (8)
I believe the answer is:
treasury
'presumably holds a number of deposits' is the definition.
I can't tell whether this definition defines the answer.
'estuary flowing around river' is the wordplay.
'flowing' is an anagram indicator.
'around' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'estuary' is an anagram of 'treasuy'.
'treasuy' going around 'r' is 'TREASURY'.
Can you help me to learn more?
(Other definitions for treasury that I've seen before include "Its valued contents" , "Finance ministry" , "thesaurus" , "The funds available to government" , "The funds of a state" .)