Arrive at open stretch of water (5)
I believe the answer is:
reach
This clue is a double definition.
'arrive at' is the first definition.
(synonyms)
'open stretch of water' is the second definition.
(I've seen this before)
(Other definitions for reach that I've seen before include "Get as far as" , "Hands up" , "Open stretch of water" , "Stretch of river: achieve" , "Arrive at (a place)" .)