Waikato's Medical Officer of Health, Dr Felicity Dumble, has issued a health warning advising people to avoid recreational contact with the Waikato River.
The warning is in place from Orakei-Korako down to Port Waikato.
Dr Dumble said the health warning has been issued because recent tests show that potentially toxic blue-green algae bloom (Anabena planktonia) is present in the River.
Algae is a naturally occurring phenomena which grows during hot and humid conditions. Most is harmless. However, current levels of the algae are very high and it has now been determined that one of the algae is potentially toxic.
At a meeting today, Waikato Regional Council (Environment Waikato) advised that algae levels were above recommended guidelines for recreational contact. Environment Waikato water quality scientist Bill Vant said levels from 16,000 to 35,000 cells /mL have been found at different testing sites along the River.
Current guidelines for recreational contact indicate that a health warning be issued once levels had reached 15,000 cell/mL.
Environment Waikato is now regularly testing for these specific algal levels in addition to its normal testing regime.
"We will know whether or not toxins are present in the River by early next week. At this stage, all we can be certain of is that blue-green algae levels are high," Dr Dumble said.
A similar health warning was issued yesterday by Pacific Health concerning the same algae in Lake Rotoiti near Rotorua.
Dr Dumble said that people should not drink untreated water from the River, but that at this stage, treated water supplies were still considered safe. The public health unit was working closely with local councils, including Hamilton City Council, to monitor drinking water standards.
The recent odour and taste issues with Hamilton's drinking water are directly related to the algae bloom, she said.
"Hamilton City is working closely with us and the Regional Council and has been very proactive in putting extra precautions in place. At this stage, it is considered safe to drink Hamilton's treated water," Dr Dumble said.
Toxins in the water can lead to health problems in some circumstances when water is swallowed or comes into contact with skin. Symptoms can include minor skin rashes. In susceptible people, the toxins may set off asthma or hay fever attacks. Severe reactions are uncommon.
"We haven't had any notifications of any illness from exposure to or ingestion of the water, but a risk is present while algae levels remain high and we are being cautious."
At a joint meeting today, Dr Dumble advised councils to erect warning signs along the River – particularly in key recreational areas.
"We are working jointly on this issue and councils are taking a very positive and proactive approach," Dr Dumble said.
City and district councils which take drinking water from the River have begun carrying out detailed risk assessments of their water supplies, she said.
"We will continue to monitor the situation closely until the algae returns to safe levels. At that point, we will resume normal surveillance and testing regimes."