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.

Read more about blue-green 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.

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Current Status

The Waimea River at River Rd 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 SampledCoverageComments
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
4 January 2017 <1% No sign of toxic algae
28 December 2016 <1% No sign of toxic algae
22 December 2016 <1% No sign of toxic algae
20 December 2016 <1% No sign of toxic algae
15 December 2016 10% Moderate phormidium cover
13 December 2016 5% Low phormidium cover
6 December 2016 <1% No sign of toxic algae
29 November 2016 5% Low phormidium cover
22 November 2016 5% Low phormidium cover
1 March 2016 <1% No sign of toxic algae

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Roding River at Twin Bridges

Date SampledCoverageComments
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
4 January 2017 <1% No sign of toxic algae
28 December 2016 <1% No sign of toxic algae
22 December 2016 <1% No sign of toxic algae
20 December 2016 <1% No sign of toxic algae
15 December 2016 <1% No sign of toxic algae
13 December 2016 <1% No sign of toxic algae
6 December 2016 <1% No sign of toxic algae
29 November 2016 5% Low phormidium cover
22 November 2016 5% Low phormidium cover
1 March 2016 <1% No sign of toxic algae

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Takaka River at Reilly Street

Date SampledCoverageComments
12 January 2016 1% Low phormidium cover

Takaka River at Top Rocks

Date SampledCoverageComments
4 January 2017 <1% No sign of toxic algae
28 December 2016 <1% No sign of toxic algae
22 December 2016 <1% No sign of toxic algae
20 December 2016 10% Moderate phormidium cover
15 December 2016 <1% No sign of toxic algae
13 December 2016 <1% No sign of toxic algae
6 December 2016 <1% No sign of toxic algae
29 November 2016 <1% No sign of toxic algae
22 November 2016 <1% No sign of toxic algae

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 Waimea River at River Rd 

Date SampledCoverageComments
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
4 January 2016 2% Low phormidium cover
28 December 2016 <1% No sign of toxic algae
20 December 2016 2% Low phormidium cover
13 December 2016 <1% No sign of toxic algae
6 December 2016 <1% No sign of toxic algae
22 November 2016 <1% No sign of toxic algae

Waimea River at SH60 Appleby

Date SampledCoverageComments
1 March 2016 <1% No sign of toxic algae

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Wai-iti River at Brightwater Bridge

Date SampledCoverageComments
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
28 December 2016 15% Moderate phormidium cover
20 December 2016 10% Moderate phormidium in riffles
13 December 2016 1% Low phormidium cover
6 December 2016 <1% No sign of toxic algae
22 November 2016 <1% No sign of toxic algae

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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 eat any algae).

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