Olympic figure skater Johnny (4)
I believe the answer is:
weir
'olympic figure skater johnny' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for weir that I've seen before include "Small dam built across river to regulate flow" , "fish may be trapped in this enclosure" , "Dam on a stream to control water level or flow" , "Barrier" , "River flow regulator" .)