Rush to get deer standing (4)
I believe the answer is:
reed
'rush' is the definition.
(plants found by water)
'deer standing' is the wordplay.
'standing' says the letters should be written backwards (in a down clue, letters stand up).
'deer' backwards is 'REED'.
'to get' acts as a link.
(Other definitions for reed that I've seen before include "Type of grass" , "Plant of marshy land" , "Tall grass of wet areas" , "Vibrator in the mouthpiece of a wind instrument" , "'It vibrates in a clarinet, say (4)'" .)