UPDATE - 17 February 2010
The warning on water quality at Dudding Lake has been lifted.
UPDATE - 12 February 2010
From Barry Gilliland - Horizons Regional Council.
This week's sample was taken on Monday 8 February:
Basically the cell numbers and toxin levels have dropped away so it is looking good for the public health warning to be lifted after next week's sample…assuming the current trend continues!
The details are: I detected no odour on opening the sample bottle. The water itself looked clear, but when I looked closely there was a low density of particles of varying sizes present. There was no evidence surface scumming in the sample.
Under the microscope I saw colonies of two types blue-green algae: Anabaena sp and Microcystis spp (two different species). The cell numbers were dominated by Microcystis spp. I estimate the cell density to be 2,517 blue-green algal cells per millilitre.
I also have the results of two toxin tests on the sample. A quick test strip test gave an indicative result of 2.5ug total microcystins/L and the ELISA test done by AgResearch gave a result of 1.3ug total microcystins/L. Both the toxin results indicate levels of microcystins have fallen below the NZ guideline value of value of 12 ug total microcystins/L. Although this is great news, the normal process is to wait for two consecutive results that meet the guideline before warnings are lifted. That means we await the results of this coming Monday with real interest. In the meantime the public warning for the lake remains in place.
29 January 2010
Tests carried out by Horizons Regional Council have shown elevated concentrations of cyanobacterial toxins (caused by blue-green algae) at Dudding Lake, near Marton, and a health warning has now been issued.
Visitors to the Lake are advised not to use the water body for recreational purposes until health warnings are removed.
Cyanobacteria produce toxins that are harmful to humans and animals if swallowed or through contact with skin (such as may occur when swimming, water skiing or kayaking).
Exposure to cyanobacteria may cause symptoms such as skin rashes, nausea, tummy upset and tingling and numbness around the mouth or tips of fingers.
If you experience health symptoms after contact with contaminated water, visit a doctor immediately. Boiling water does not remove toxins and drinking of the water should be avoided at all times.
Fish and shellfish can concentrate toxins and their consumption should be avoided. If fish are eaten, remove the gut and liver and wash in clean water.
Cyanobacteria occur naturally but can increase rapidly during summer. If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
Not all cyanobacterial blooms are visible and toxins can persist after the bloom has disappeared. Cyanobacterial concentrations can change quickly with changing environmental conditions (eg, wind). If a health warning is in place, avoid contact with the water.
Horizons Regional Council monitors cyanobacteria at Duddings Lake during summer and the public will be advised of any changes in water quality that are of public health significance.
Contact:
Bruce Butters, Health Protection Officer, MidCentral Health, Wanganui Hospital on 06 348 1234 or MidCentral Communications Unit 06 350 8900.
