An expert in Canterbury waterways says Christchurch's city rivers are being choked with about 5000 cubic metres of untreated sewage and waste water per day.
He said delays to the rebuild of Christchurch's sewer system are causing the problem.
Bryan Jenkins, professor of strategic water management at the Canterbury University, said during the peak of the earthquake aftermath, the overflow sat at about 85,000 cubic metres per day.
He said that had reduced to about 5000 cubic metres per day by September 2011, and any discharge which now occurred happened intermittently.
However, simply repairing and replacing the city's damaged infrastructure was not a safe enough measure.
"Overflow storage before it gets into the river system is one option. Constructed wetlands and removal of any spills is certainly another approach.
"There are a number of things that can be done to actually improve the situation for Christchurch."
Professor Jenkins said the bacterial and viral content of the Avon and Heathcote rivers made them too unhealthy for recreational use.
