The deaths of two dogs in Mosgiel is being blamed on toxic algae.

Toxic algae has appeared in a number of areas around New Zealand this summer, prompting warnings to parents and pet owners, and during the past few years it has claimed the lives of many dogs.

Otago Regional Council director of environmental information and science Dr John Threlfall told the Otago Daily Times last night he was still awaiting the result of tests.

However, it was probable the dogs had swallowed the algae Phormidium while drinking from the low-flowing Silver Stream.

The black, shiny algae gives off a toxin and Dr Threlfall said it could be harmful to humans.

"Caregivers should supervise young children playing close to the Silver Stream to ensure they don't touch or eat any algal material.

"Dog owners should also keep their pets clear of the river."

Otago medical officer of health Dr Derek Bell said the algae could cause allergic reactions including asthma, eye irritations, rashes, blistering around the mouth and nose and gastro intestinal disorders including abdominal pain, cramps and diarrhoea.

He advised anyone affected to seek medical advice.