A report from Leisure Engineering, released yesterday, concluded the fast slide should not be operated until alterations were made to a portion of it.
It said the slide was not inherently safe and had to be ridden in a fully reclined position.
However, the slide caused a reflex action in riders to try to sit up.
"It is not reasonable to expect patrons to recline for the whole slide journey, given the abrupt direction changes and the awkward positioning of riders induced by the geometry of the slide," it said.
It also said the slide's gradient, severity of the changes of direction and water flow rates could be altered to make the ride safer because, even lying down, riders could be injured.
"There is no means of enforcing the reclined position once the rider has departed . . .
"There is no comprehensive assurance in the controlled testing that some riders will not be tipped in the slide, even if adhering to the fully-reclined position, such is the impact on the rider of the sudden changes of direction experienced in the slide," it said.
A dive instructor was injured testing the hydroslide while researching the report.
The instructor had attempted riding in a sitting position, overturned and received a minor injury.
The Queenstown Lakes District Council commissioned the review after a woman complained to the Department of Labour about receiving minor concussion and injuring her shoulder on the slide on May 17.
The slide was closed in June while Australian company Leisure Engineering carried out the review.
It was the second time the slide had to be closed because of safety concerns.
It was closed on December 9 last year after Lakes Leisure confirmed up to 69 customers had received minor injuries since it opened on May 31, 2008.
Queenstown Lakes District Council capital works manager Ken Gousmett said the report outlined several modifications which should overcome safety concerns.
It had not been decided which modifications would be made.
Naylor Love, the aquatic centre's main contractor, and Aeromarine Ltd, the designer and hydro slide builder, were now considering the options.
They would also bear the cost of the changes.
"At this stage, I am hopeful that the modification can be under way shortly but I'm not able to identify a time frame as yet," Mr Gousmett said.
