A Christchurch schoolboy drowned after his family mistook a water-safety sign for an indication the river was safe.

A coroner's report released yesterday said Haenga Puhupuhi-Albert, 15, drowned on a family trip to the Waimakariri River on February 23, 2010.

Haenga had been swimming with his family on an outing after he finished school, on the north side of the river near the old Waimakariri Bridge.

He had been trying to swim to the south bank when he was caught by the current and dragged under. He did not resurface. His body was found in the river the following day.

Haenga's father said many people were swimming in the same place, and no signs indicated there was any danger. They had noted one sign reading: "Beware strong currents. Think water safety if swimming."

It showed a picture of a swimmer with an arrow pointing to the water, but they thought it meant the Waimakariri was a swimming river.

Coroner Sue Johnson agreed the sign was misleading. It had since been replaced with a large sign on a bridge pile declaring the river unsafe for swimming.

Similar signs had been erected at various other places around the area.

The area was the same spot that claimed the lives of Lale Sioa Taiulu, 16, and Larry Pau, 26, in 2008, and Afghan refugee Rahmahullah Qumbari, 23, in 2004.

The coroner said Haenga's death was an example "of how recreation in water can quickly turn from pleasure to tragedy".

"Haenga was not a good swimmer and when he went under he failed to resurface.

"His death is a tragedy and his loss has devastated his family."

She noted that there had been no further drownings in the river since the new signs were erected.

"The new signs put up by ECan after Haenga's death will go a long way to prevent further deaths," she said.

"The Waimakariri is not a safe swimming river, especially by its bridges and . . . people should not ignore the signs advising not to swim there."

- © Fairfax NZ News