Property manager ' />

The man responsible for 640 litres of hydraulic oil spilling into the Waikato River has come clean to say he is "deeply sorry".

Property manager Steve McLennan, a former Hamilton city councillor, blew the whistle on himself after learning that a plumbing malfunction in the Tower Building on Ward St caused the oil spill on Saturday morning.

Mr McLennan manages the building on behalf of its owner, Waiheke Island farmer Chris Reeve.

A member of the public notified the Waikato Regional Council after seeing a large oil slick flowing into the river near Claudelands Bridge from a stormwater drain.

Mr McLennan yesterday apologised to the city council, regional council and visited the Waikato River Authority office to apologise, as well as emailing the 30 tenants of the building.

"It's embarrassing for them to be associated with a building that caused a leak like this," he said.

Mr McLennan said he confessed after learning the oil had gone into the river and not the sewerage drain - as he had been initially told.

"We are fully prepared to face the music. We did nothing to precipitate this. We do everything we can to make sure our buildings are safe. It's an unforeseen tragedy ... we are deeply sorry."

The error occurred on Friday night after the ballcock valve in one of the three water tanks broke, causing it to overflow across the carpark in the lower basement and into the lift shaft.

The sump pump could not push the water out fast enough and the overflow began to cover the hydraulic buffer, which contains 640 litres of oil.

As a result, the fluid ran into a stormwater drain in Worley Place which discharges into the river.

The ballcock valve had been replaced in November and Mr McLennan was working with plumbers to install early warning systems.

"We are doing everything we can to make sure it doesn't happen again. We are very upset," said Mr McLennan.

Waikato Regional Council compliance and education manager Rob Dragten thanked Mr McLennan for owning up to the spill and said the council would decide whether to prosecute when the investigation was completed.

Mr Dragten said the council would have to consider whether the statutory defence of an unforeseen mechanical failure leading to a discharge could be applied under the Resource Management Act.

Mr McLennan said he felt like "lightning had struck twice". In 2009, he was forced to apologise after the wrong application of a bird repellent killed more than 70 swallows.

The birds became stuck to a pipe on a Garden Place building after too much Hot Foot gel was applied.