Ringed zone around old lake and river (7)
I believe the answer is:
areolar
'ringed zone' is the definition.
'areolar' can be an answer for 'ringed' (relating to areoles). I am unsure of the 'zone' bit.
'around old lake and river' is the wordplay.
'around' means one lot of letters goes inside another.
'old' becomes 'o' (abbreviation).
'lake' becomes 'L' (geographical abbreviation).
'and' means one lot of letters go next to another.
'river' becomes 'arear' (I can't explain this - if you can you should give a lot more credence to this answer).
'o'+'l'='ol'
'ol' going within 'arear' is 'AREOLAR'.
Can you help me to learn more?
(Other definitions for areolar that I've seen before include "about a pupil" , "of circular area" .)