The river runs through the 243ha Whitiau Scientific Reserve. Once completed, the trail will follow the coast from South Beach to Turakina Beach.
Walkers currently have to use about 32km of roads, including State Highway 3, between Whanganui and Turakina.
Trail chief executive Matt Claridge said the trust would like to raise $150,000 from the public, with the rest coming from grants and other fundraising.
Mike Tweed is a multimedia journalist at the Whanganui Chronicle. Since starting in March 2020, he has dabbled in everything from sport to music. At present, his focus is local government, primarily Whanganui District Council.