Toxic algae monitoring results

The Ministry for the Environment (MfE) cyanobacteria guideline survey method is being used for assessment. Ministry guidelines state that warning signs should be put up around rivers where the percentage coverage of toxic algae is above 20%.

Where levels are below 20% and there is no need for warning signs. We would still recommend that the public keep an eye on children and dogs near the water - don’t let them eat any algae. 

During extended summer low flows some naturally-occurring blue green algae (cyanobacteria) can increase cover of the stream bed and produce toxins which, if consumed in high enough quantities, can cause illness or death. Phormidium is the main toxin-producing cyanobacteria.

A confirmed toxin-producing blue-green alga was present in the lower Waimea River in January 2014. Other rivers in Tasman District had toxin producing algae during the 2012/2013 summer season. As a result of this, the rivers are being monitored for the presence of blue-green algae and the results are shown below.

In Tasman District there have been no cases of human sickness or death due to toxic algae. However, there have been cases of dog death where toxic algae was suspected as the cause. Dogs, puppies in particular, are most vulnerable to these toxins because they will drink from rivers and consume algae either attached to the riverbed or floating. One case, in late January 2013, occurred when the coverage of toxic algae on the bed was very low (2.5%), which suggests that there is a risk to dogs at almost any time.