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Toxic Algae Monitoring
This page lists results of toxic algae monitoring in the district's rivers. Rivers are monitored at times of risk of algal build up.
Current Status
The Waimea River at River Road and several popular swimming sites are being monitored weekly for signs of toxic algae. Visual estimates of percentage coverage are shown below:
Lee River at Lee Reserve
| Date Sampled | Coverage | Comments |
|---|---|---|
| 28 February 2017 | <1% | No sign of toxic algae |
| 21 February 2017 | <1% | No sign of toxic algae |
| 14 February 2017 | <1% | No sign of toxic algae |
| 7 February 2017 | <1% | No sign of toxic algae |
| 31 January 2017 | <1% | No sign of toxic algae |
| 24 January 2017 | <1% | No sign of toxic algae |
| 17 January 2017 | <1% | No sign of toxic algae |
| 10 January 2017 | <1% | No sign of toxic algae |
| 5 January 2017 | <1% | No sign of toxic algae |
Roding River at Twin Bridges
| Date Sampled | Coverage | Comments |
|---|---|---|
| 28 February 2017 | <1% | No sign of toxic algae |
| 21 February 2017 | <1% | No sign of toxic algae |
| 14 February 2017 | <1% | No sign of toxic algae |
| 7 February 2017 | <1% | No sign of toxic algae |
| 31 January 2017 | <1% | No sign of toxic algae |
| 24 January 2017 | <1% | No sign of toxic algae |
| 17 January 2017 | <1% | No sign of toxic algae |
| 10 January 2017 | <1% | No sign of toxic algae |
| 5 January 2017 | <1% | No sign of toxic algae |
Takaka River at Reilly Street
| Date Sampled | Coverage | Comments |
|---|---|---|
| 12 January 2016 | 1% | Low phormidium cover |
Takaka River at Top Rocks
| Date Sampled | Coverage | Comments |
|---|---|---|
| 4 January 2017 | <1% | No sign of toxic algae |
Waimea River at River Rd
| Date Sampled | Coverage | Comments |
|---|---|---|
| 2 March 2017 | 2% | Low phormidium cover, but thick, isolated patches in riffles |
| 21 February 2017 | 1% | Low phormidium cover in riffles |
| 14 February 2017 | 1% | Low phormidium cover in riffles |
| 7 February 2017 | <1% | No sign of toxic algae |
| 31 January 2017 | <1% | No sign of toxic algae |
| 24 January 2017 | 2% | Low phormidium cover |
| 17 January 2017 | 2% | Low phormidium cover |
Waimea River at SH60 Appleby
| Date Sampled | Coverage | Comments |
|---|---|---|
| 2 March 2017 | 2% | Low phormidium cover, but thick, isolated patches in riffles |
Wai-iti River at Brightwater Bridge
| Date Sampled | Coverage | Comments |
|---|---|---|
| 28 February 2017 | 2% | Low phormidium cover in riffles |
| 21 February 2017 | 2% | Low phormidium cover in riffles |
| 14 February 2017 | 5% | Low phormidium cover |
| 7 February 2017 | 2% | Low phormidium cover in riffles |
| 31 January 2017 | <1% | No sign of toxic algae |
| 24 January 2017 | 7% | Low phormidium cover |
| 19 January 2017 | 13% | Moderate phormidium cover |
| 17 January 2017 | 16% | Moderate phormidium cover |
| 4 January 2017 | 19% | Approaching Amber alert level |
About the Sampling
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.
Risks of Toxic 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 several recent 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.