Diligent musical group ahead of us on river (11)
I believe the answer is:
industrious
'diligent' is the definition.
('industrious' can be similar in meaning to 'diligent')
'musical group ahead of us on river' is the wordplay.
'musical group' becomes 'trio' (trio is a kind of musical group).
'ahead of' is a charade indicator (letters next to each other) (I've seen this in other clues).
'on' says to put letters next to each other.
'river' becomes 'indus' (Indus River is an example**).
'trio'+'us' is 'trious'.
'trious' after 'indus' is 'INDUSTRIOUS'.
(Other definitions for industrious that I've seen before include "Busy" , "Toiling hard" , "Diligent, hard-working" , "Hard working" .)