Swimmers enjoying Canterbury's open water this weekend are being urged to check before they dive, as many beaches and rivers remain unsuitable for swimming.
Te Whatu Ora warned a number of sites within Lyttelton and Akaroa Harbours, including popular spots like Akaroa Main Beach, Corsair Bay, Rāpaki Bay, Sandy Bay, Diamond Harbour Beach and Purau Beach Rāpaki Bay, were unsafe to swim in due to the poor water quality.
The health agency said up-to-date information about the safety of swimming spots could be found on the Land Water Aotearoa website.
Canterbury medical officer of health Cheryl Brunton said the Canterbury Regional Council would be testing the water weekly at the sites it monitored, and advising which waterways contained unsafe levels of bacteria or cyanobacteria (toxic algae).
"Exposure to these could be harmful to swimmers' health which means temporary health warnings may also be issued by Te Whatu Ora. That's why it's really important to check that it is safe to swim at your favourite spot before you jump in.
"After heavy rain, other recreational water sites are also likely to be contaminated from rural and urban run-off.
"As a precaution, avoid swimming in the harbour, rivers, streams, lakes or estuaries for at least 48 hours after heavy or prolonged rainfall, even at sites that usually have good water quality."
Brunton said people should also avoid eating shellfish from the harbour after heavy rainfall.