Care about learners on river in calm water? (8)
I believe the answer is:
millpond
'calm water?' is the definition.
'care about learners on river' is the wordplay.
'care' becomes 'mind' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'learners' becomes 'll' (two abbreviations for learner).
'on' says to put letters next to each other.
'river' becomes 'Po' (Italian river).
'll'+'po'='llpo'
'mind' enclosing 'llpo' is 'MILLPOND'.
'in' is the link.
(Other definitions for millpond that I've seen before include "Proverbially placid water" , "this is traditionally flat" .)