A report into Christchurch's Heathcote and Avon river catchments has described them as significantly degraded.
The study was commissioned by the Canterbury regional council, Ecan, for its River Guardians Project.
It says water quality in both catchments is of low quality, and that sedimentation, nutrient enrichment, toxic pollution and faecal contamination are all serious problems.
The Avon-Heathcote Estuary Ihutai Trust chairperson, Alex Drysdale, says faecal contamination causes sickness in people and can kill wildlife.
He says he is relieved to finally have data confirming what he has long suspected, and hopes the report will encourage companies and individuals to think more about the way they dispose of waste water.