A health warning has been issued for the South Island's Hurunui River at the Balmoral swimming hole.
The warning on Wednesday follows findings of high levels of potentially toxic blue-green algae in the river, which is currently present in low-flowing channels near State Highway 7.
The Canterbury District Health Board is warning people and their animals, particularly dogs, to avoid the area of the river until the health warning has been lifted.
The algae looks like dark brown to black mats and can produce toxins harmful to people and animals, says Canterbury Medical Officer of Health Dr Alistair Humphrey.
"Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips," Dr Humphrey said.
"If you experience any of these symptoms, visit your doctor immediately. Also let your doctor know if you've had contact with dark brown/black algal mats or water in this area."
The algae often accumulates at shallow, slow flowing areas on the edge of the river, so even paddling in the shallows should be avoided.
Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.
There is also a warning against swimming, fishing or taking water from part of Lake Dunstan in Central Otago is still in place as the cause of high levels of E.Coli remains unknown.
Water samples from the Bendigo freedom camping site have shown high readings of E.Coli in the Bendigo area of the lake, Land Information NZ says.
LINZ was closing off the toilet block as a precaution until the source of the contamination could be determined, and four additional portaloos were brought in.
BLUE-GREEN ALGAE FACTS
* Looks like dark brown/black mats attached to rocks along the riverbed
* It occurs naturally but can increase rapidly during warmer months
* It has a strong musty smell
* Detached mats can accumulate along the shore and increase the risk of exposure to toxins
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