Turn river into land (6)
I believe the answer is:
sprain
'turn' is the definition.
('sprain' can be a synonym of 'turn')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for sprain that I've seen before include "Pull" , "Turn" , "Wrench (a ligament) (P, not T)" , "Injure joint by wrenching it violently" , "Injury to ligaments" .)