Whitebaiters looking forward to the opening of the new season tomorrow have been warned to avoid Christchurch's rivers due to faecal contamination.
Health experts said even before the earthquakes, the Garden City's waterways were contaminated with duck and dog faeces and rarely met recreational water standards.
But since the quakes, and more recently because of ongoing repairs to damaged wastewater infrastructure, there is an additional risk of human faecal contamination.
Canterbury medical officer of health, Dr Alistair Humphrey said eating whitebait caught in Christchurch's Avon and Heathcote rivers and the Avon-Heathcote Estuary is dangerous.
"People who choose to take whitebait from the Avon or Heathcote not only put themselves and others at risk but also spoil the season for other whitebaiters and consumers, as it makes us question whether any whitebait is safe to eat,'' he said.
Raw sewage discharges occur into the rivers on occasions when contractors carry out essential repairs to sewers, Dr Humphrey said.
"Therefore E.coli (faecal bacteria) levels increase during this time.''
A 2013 report by ESR scientists on Avon River water, sediment and estuarine sediment also highlights ongoing water quality issues, he said.
"Water quality has improved since the active discharge period but generally does not meet the recreational water guidelines.''
"The silt in the river still contains E. coli and at one site the concentration found was 15 times more contaminated than during the active discharges.
"Giardia, Campylobacter and Cryptosporidium levels in the sediment have decreased since the previous study but are still present in varying levels. Giardia can cause explosive bloody diarrhoea for months.''
Giardia eggs can live for months or years in silt and can be released into the water when the silt is stirred up.
It can also survive freezing, so when a block of whitebait is thawed out at home, many parts of the kitchen can be contaminated, even if the whitebait is cooked.