Gains power over turbulent streams (7)
I believe the answer is:
masters
'gains power' is the definition.
The answer and definition can be both related to competing as well as being verbs in their -s form.
Perhaps you can see a link between them that I don't see?
'turbulent streams' is the wordplay.
'turbulent' indicates anagramming the letters.
'streams' anagrammed gives 'MASTERS'.
'over' is the link.
Can you help me to learn more?
(Other definitions for masters that I've seen before include "Male teachers" , "Could be checkers" , "Boys" , "competition today" , "Artists of consummate skill" .)