My call out for poems about New Zealand rivers got an immediate response! Thank you to a certain olive farmer of Awatere Valley, who alerted me to this poem by Eileen Duggan. Certainly one from the “river as a metaphor” file – for love, in this case. The metaphors come thick and fast in this one! Not really my cup of tea – perhaps I am not the romantic type.
(An interesting aside though: the map fragment in one of envirohistory NZ’s revolving banners is of the Wairau Bar, which the poet draws on for her stream of metaphors (see what I did there?!) Learn more about this river’s fascinating pre-European history in this post.)
The tides run up the Wairau
The tides run up the Wairau
That fights against their flow.
My heart and it together
Are running salt and snow.
–
For though I cannot love you,
Yet, heavy, deep, and far,
Your tide of love comes swinging,
Too swift for me to bar.
–
Some thought of you must linger,
A salt of pain in me,
For oh what running river
Can stand against the sea?
envirohistory NZ 
The poem uses the contrary forces of the river and tide with moving effect.