Bacteria levels at rivers and lakes in Otago
Rachel Ozanne, Environmental Resource Scientist:
The week’s water quality monitoring has returned high levels of bacteria in a number of rivers and lakes. The following waterways have reached a level where it is currently unsuitable for swimming and contact recreation.
Cyanobacteria reported in Lake Hayes
This week’s water quality testing from Lake Hayes shows that cyanobacteria in the Lake has increased significantly. Water sampling on Monday 5 March returned a biovolume for cyanobacteria at 11.04 mm3/L. This is an increase from the previous week’s result where the cyanobacteria biovolume was measured at 1.05 mm3/L. Cyanobacteria scums are particularly prevalent at the Mill Creek/Campground end of the Lake. Swim warning signage was placed at the Lake yesterday.
Government water quality guidelines for recreational swimming areas are that those with a cyanobacteria biovolume less than 0.5 mm3/L should be safe for swimming. Whereas water with a biovolume of more than 1.8 mm3/L indicates a potential health risk. It is recommended that people avoid contact recreation in the lake for now.
For dog owners, when a cyanobacteria alert is in place, it is important that dogs are kept on a lead, out of the water and that they do not consume vegetation from the water’s edge. Signs that a dog has been poisoned by toxic algae can include lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsions. It is important to treat the first signs of illness as an emergency and contact your vet immediately.
E. coli reported at Frankton Bay – Lake Wakatipu
Otago Regional Council (ORC) water quality samples taken from Frankton Bay at Lake Wakatipu have shown high levels of the bacteria E. coli. Water sampling on Monday 5 March showed E.coli levels at 1414 E. coli/100 ml. The cause of the bacteria is currently under investigation.
Government water quality guidelines for recreational swimming areas are that those with less than 260 E. coli/100 ml should be safe, whereas water with more than 550 E. coli/100 ml indicates a potential health risk. Signage advising against swimming has been installed at Frankton Bay yesterday, with additional signage to be installed today.
E. coli reported at Manuherikia River
ORC water quality samples taken from Manuherikia River at Shaky Bridge have shown high levels of the bacteria E. coli. Water sampling on Monday 5 March showed E. coli levels at 866 E. coli/100 ml. The brown discoloured water in Manuherikia River is due to recent high flows and heavy rainfall.
Government water quality guidelines for recreational swimming areas are that those with less than 260 E. coli/100 ml should be safe, whereas water with more than 550 E. coli/100 ml indicates a potential health risk. Signage advising against swimming has been installed at Manuherikia yesterday, with additional signage to be installed today.
Additional rivers and estuaries
There are a number of other rivers and estuaries in the Otago region which are also showing elevated levels of bacteria this week. This is due to heavy rainfall last week. ORC would like to remind people to be careful of recreating in or around waterways for 48 hours following rainfall as it is common for bacteria levels to be increased. Please check the LAWA’s ‘Can I Swim Here’ website regularly to stay informed about water quality levels around the region: www.lawa.org.nz/swim
Statement from Southern DHB
Southern DHB Medical Officer of Health, Dr Keith Reid, says people should avoid swimming in areas with elevated levels of E. coli or cyanobacteria until water sampling tests indicate it is safe.
Exposure to E. coli can result in gastroenteritis symptoms within 12 to 18 hours of exposure.
“Anyone who swims in the area should wash down with soapy water,” Dr Reid said. “Limiting exposure and practicing good hand hygiene remains the best defence against infection of this kind.”
Exposure to cyanobacteria in humans may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers. Anyone experiencing health symptoms after contact with contaminated water should visit their doctor. Southern DHB Medical Officer of Health can be contacted on (03) 474 0999 to provide health professionals with information about those symptoms.