Cantabrians are being warned to avoid some of the region’s rivers this summer due to toxic algae.

Hot and dry temperatures in the region are expected to cause algae bloom, which can be harmful to humans and animals.

If exposed, ” [swimmers] can have respiratory symptoms, they can get rashes, nausea, sometimes stomach cramps and diarrhoea and sometimes also numbness around the mouth,” Dr Cheryl Brunton, Canterbury medical officer of health, said.

The algae dislodge easily from rocks, drifting to the edge of rivers where both children and dogs play.

“Unfortunately, it’s an odour that dogs really like, and they will go hunting it out,” Brunton said.

“Taking a piece of the algae, only a 50 cent piece in size, would kill the average dog.”

Of the 110 sites monitored in Canterbury, 40 have been deemed unsuitable for swimming, with 14 having algae warnings in place.

Environment Canterbury’s Shirley Haywood said current conditions were “perfect” for algae growth.

“We’ve had some fabulously hot sunny days, not much rain recently, not enough to cause those flows to rise.”

People were encouraged to check Land Air Water Aotearoa’s website to see which waterways were safe to swim.