Officer allowed in river, uncovering parts of jugs (9)
I believe the answer is:
Here is my best explanation:
'uncovering parts of jugs' is the definition.
(decollete refers to a low neckline)
'officer allowed in river' is the wordplay.
'officer' becomes 'col' (I've seen this before).
'allowed' becomes 'let' (I've seen this before).
'in' is an insertion indicator.
'river' becomes 'dee' (River Dee).
'collet' going into 'dee' is 'DECOLLETE'.
(Other definitions for decollete that I've seen before include "baring chest", "Low cut", "With a low neckline", "exposing milk suppliers", "Of clothes, low-cut", "low-cut dress!" and "Having a low neckline, from French".)