The lower Whanganui River has changed a lot from its days as a deep water port - mainly because it is carrying so much silt now.
Whanganui ecologist and ornithologist Peter Frost spoke about the river at the Coastal Restoration Trust's annual conference on Friday, its final day.
Frost said the Whanganui was the third-longest river in New Zealand, and the longest navigable, with 230 navigable kilometres between Whanganui and Taumarunui.
"It was the State Highway 1 of the 19th century and earlier."
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The river used to be deeper and provided a major port. That was no longer possible, partly because of the 4.7 million tonnes of sediment that moved through its mouth every year, Frost said.
He talked about other changes that had degraded the estuary as an ecosystem, and questioned whether it could be managed better.
After his talk, the conference moved to Turakina Beach to hear about the Koitiata wetlands restoration project.
About 110 people attended the conference, and Horizons Regional Council was its major sponsor. The trust looks for cost-effective and practical ways to restore coastal ecosystems.
Its conferences provide an opportunity for like-minded local people and experts to come together and discuss issues, chairman Greg Bennett said.