Scientists say it will take years to fix damage caused by the Canterbury earthquakes to waterways.
Scientists met in Lincoln on Thursday to give a free public seminar on how the quakes have affected water systems. They say liquefaction is choking riverbeds and starving aquatic life.
Jon Harding, a lecturer at Canterbury University, has been studying the impact increased levels of silt and sediment are having on the tributary rivers that flow into the Avon and Heathcote rivers.
He says in some cases, the impacts have been devastating to the feeding and breeding grounds of all levels of life - from microscopic insects to eels and trout.
Mr Harding says river dredging may be the solution, but it is also destructive.
Meanwhile, Environment Canterbury's director of investigations and monitoring says contamination caused by the Christchurch City Council discharging raw sewage into waterways has largely disappeared.
Ken Taylor says the hazard now is coming from the vast tracts of silt blocking rivers and streams and killing off the food chain.
Environment Canterbury is identifying the most important breeding sites to clear.
