Wants river to flow round between poles (5)
I believe the answer is:
needs
'wants river' is the definition.
'needs' can be an answer for 'wants' ('need' can be a synonym of 'want'). I am not certain of the 'river' bit.
'flow round between poles' is the wordplay.
'flow round' becomes 'eed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'between' is an insertion indicator.
'poles' becomes 'NS' (North and South poles).
'eed' placed within 'ns' is 'NEEDS'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for needs that I've seen before include "Wants, requires" , "What is required" , "Necessities" , "Calls for" , "shopping-list, say" .)