Four people, including a child, were dumped into the Whanganui River when a boat overturned.
The 5m aluminium boat capsized near Q-West Boat Builders in Gilberd St on Sunday afternoon.
"They were trying a tight turn and it just kept going," Coastguard Wanganui president Garry Hawkins said.
All four in the boat were wearing lifejackets. They were picked up by another nearby vessel and taken to the wharf.
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Coastguard had an ambulance at the wharf waiting to check them out.
Meanwhile, the Coastguard boat went to the aid of the upturned vessel, righted it with the help of another boat and easily towed it to shore.
It was a quick and calm rescue, Hawkins said, aided by smooth and concise communications and work from the on-call crew and radio operators.
"While our crew are trained for these situations and have experience in them, we are very grateful for help from the public, including those on the ramp, who helped."
He thanked members of the public and the crews of two vessels, Sea Leggs and Vegabond k, for their help.