Algae alert widens to Geraldine

As summer gets into full swing, toxic algae has been found at yet another popular South Canterbury swimming spot.

Community and Public Health has issued a warning after water surveys of the Waihi River at Geraldine found relatively high levels of the potentially toxic dark algae phormidium.

The warnings came into effect last night.

There were already warnings in place for the Waihao River below Bradshaws Bridge, the Waihi River at Winchester and the Temuka River at State Highway 1.

Phormidium appears as dark brown-black mats that become attached to rocks along riverbeds. Contact by skin or swallowing can cause rashes, skin and eye irritation, allergic reactions and gastrointestinal upset.

Canterbury medical officer of health Dr Alistair Humphrey said the problem had become worse over recent summers.

"The seasons of phormidium are starting earlier and finishing later ... and nitrate loading is a big factor in this," he said.

"Unless we see improvement in farmers' practices, then this is going to be the norm. No one wants that."

Dr Humphrey said the algae did not pose a mortality risk to humans, but dogs had been known to get sick or die as a result of swallowing it. "It's not pleasant stuff."

Since Environment Canterbury (ECan) began its summer water quality monitoring season about three weeks ago, it had tested many sites. Most received a clean bill of health.

However, ECan surface water quality manager Dr Tim Davie has warned people to be careful with certain spots after rain, as faeces from stock could be washed into drains and then rivers.

Residents can check for the latest updates on swimming water quality at

The Timaru Herald