Whitebaiters are being warned against fishing in or around the Avon and Heathcote rivers in Canterbury this season.
The season is due to start tomorrow but Canterbury Medical Officer of Health Dr Alistair Humphrey said eating whitebait caught in the city's waterways was dangerous.
"People who take whitebait from the Avon or Heathcote not only put themselves and other consumers at risk but also make us question if any whitebait is safe to eat," Dr Humphrey said.
The latest concern stems from a soon-to-be released ESR report showing silt in the river may now be contaminated with oocycts (eggs) from giardia, Dr Humphrey said.
The tiny eggs could live for years in silt and released into the water when the silt was stirred up, he said.
Giardia can also survive freezing, so once thawed giardia within the whitebait can contaminate other foods.
Dr Humphrey said that even before the earthquake Christchurch's waterways rarely met recreational water standards because they were contaminated with duck and dog faeces.
Despite this, some people still collected whitebait from the Avon and Heathcote rivers but now there was the additional risk of human faecal contamination as a result of heavy rainfall and sewer pipe repair works.