Corrupt mischief-maker floating on river (6)
I believe the answer is:
impure
'corrupt' is the definition.
(I've seen this before)
'mischief-maker floating on river' is the wordplay.
'mischief maker' becomes 'imp' (I've seen this in other clues).
'floating on' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'river' becomes 'ure' (river in Yorkshire).
'imp'+'ure'='IMPURE'
(Other definitions for impure that I've seen before include "Unchaste, polluted" , "Unrefined" , "Dirty or immoral" , "Lewd" , "Sullied or adulterated" .)