Algal contamination risk in Silver Stream falls

The algal contamination found in the Silver Stream earlier this year, which can cause serious ill-effects in dogs, has declined to very low levels.

Otago Regional Council (ORC) director environmental information and science John Threlfall said higher flows and cooler weather had brought about the reduction in contamination by the cyanobacteria (or blue-green algae) known as Phormidium.

Phormidium is regularly found in Otago during the summer, is typically black and shiny, and often sticks to rocks or attaches itself to in-stream weeds. It can produce toxins which may prove fatal to dogs.

In February a local veterinarian reported two dogs dying from symptoms which could fit toxic algae ingestion. ORC staff collected samples from a section of the Silver Stream where the dogs had been walking. The Cawthron Institute subsequently confirmed the algae as Phormidium.

As a precaution, ORC staff put up signs alongside the stream, warning dog owners to keep their pets out of the water.

Dr Threlfall said the algae could not be found in the Silver Stream through Mosgiel during a recent search. Therefore the signs have been removed. However, pet owners should still be aware that the algae could be found in any stream at any time in Otago.