Toxic algae are naturally occurring. They are particularly prolific in summer when longer days and higher temperatures provide good growing conditions.
In Marlborough the most common toxic algae are Phormidium. They form dark brown mats growing on rocks in the river bed and are mainly found in fast flowing water, such as riffles. When algae mats become very thick they start to detach from the rocks and float in the water, accumulating along the edges of the river. This is when the algae present the greatest risk to recreational users and dogs.
The algae have a musty smell that dogs are attracted to. As little as an area of a 50 cent piece can be fatal to a dog when digested. The neural toxins produced by the algae cause muscular twitching, paralysis and convulsion. If your dog shows any of these symptoms after spending time in a river, take it to the vet immediately. In extreme cases, death can occur within 30 minutes after the first symptoms are noticeable. Small children are also at risk as they might accidentally ingest the algae when playing in the water.
In a number of neighbouring regions toxic algae mats have caused several dog deaths. Although there have been no confirmed cases in Marlborough, we have seen an increase in the occurrence of toxic algae mats in our streams and rivers.
This is a very wide-spread phenomenon and Council is unable to place warning signs at all sites with toxic algae. It is therefore important that you familiarise yourself with what these algae look like and keep children and dogs away from rivers with toxic algae.
There are many different kinds of algae that grow in rivers, but toxic algae have a quite distinct appearance. Below is a link to a video made by Cawthron and pictures of toxic algae from Marlborough rivers to help you with the identification.
If you suspect that you dog or child has ingested toxic algae visit your doctor/vet immediately.