Blue-green algae present in Hutt River
Greater Wellington and Regional Public Health are advising the public to take care around parts of the Hutt River, following increased growth of potentially toxic blue-green algae.
Weekly monitoring by staff from Greater Wellington and local councils has identified moderate growth of the algae in the Hutt River in the vicinity of the Silverstream railbridge and areas downstream. Medium risk warning signs are being posted today in these areas to alert river users.
We use a two-tiered warning sign system to advise river users of the risk from toxic algae,” Greater Wellington environmental scientist Summer Warr says. The warning system is based on river bed coverage and algal mat exposure and follows the recently released New Zealand Guidelines for Cyanobacteria in Recreational Fresh Waters.
“A medium risk sign means users can still swim or walk their dogs but should check first for any algal mats. To help people identify what the algae looks like GW has placed pictures on their website. A high risk sign means people should avoid contact recreation and dog walking in that part of the river,” she says.
Blue-green algae are microscopic organisms that are naturally present in many New Zealand waters, including relatively ‘clean’ waters. Algal growth increases when river flows are low and stable and temperatures consistently warm.
Blue-green algal mats are actually a dark brown or black colour and grow as a thick layer on rocks in the riverbed. Continuing warm and dry weather combined with low river flows may mean that the algal mats become exposed or easily accessible to dogs, stock and recreational users.
The toxins produced by blue-green algae can be fatal to dogs, which are particularly susceptible to exposure because they like to scavenge near water. Contact with blue-green algae toxins may also cause vomiting, diarrhoea and skin irritations in humans.
Rivers users - particularly those with dogs, those swimming, or drawing water from the river for stock/human consumption - should be on the look out for exposed or easily accessible algal mats and avoid any contact with them or water in the area.
More information about toxic algae, including pictures and current warnings, can be found at www.gw.govt.nz/toxic-algae. If you see any exposed or easily accessible algal mats, contact Greater Wellington on P 04 384 5708, or an environmental health officer at your local council.
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Blue green algae – Q & A
What are blue-green algae?
Blue-green algae (or cyanobacteria) are microscopic organisms that are naturally present in many New Zealand waters, including relatively ‘clean’ waters. Like other algae, growth of blue-green algae is encouraged when river flows are low and stable and temperatures consistently warm.
What do they look like?
Blue-green algal mats are actually dark brown or black and grow attached to rocks on the river bed. Mats that come loose from the river bed can wash up on the river bank or form floating ‘rafts’ in shallow areas. Where exposed, the mats may dry out and turn a light brown or white colour. They may also produce a strong musty odour.
Blue-green algae differ from harmless bright green algae, which often form long filaments. Mats of light brown or olive green algae are also harmless.
What is the problem with blue-green algae?
Some algal mats produce toxins that can be harmful to humans, dogs, livestock and wildlife. Five dogs died in the summer of 2005/06 and several died in the summer of 2007/08 after ingesting algal mats along the edge of the Hutt River.
What are the possible health effects?
Swallowing water containing blue-green algae toxins can lead to vomiting, diarrhoea, abdominal pain, cramps, nausea and other effects in humans. Skin contact can cause irritation of the skin, eyes, nose and mouth. Exposure to high levels of toxins can result in serious illness or death. Dogs are particularly susceptible to poisoning from blue-green algae as they love to scavenge and play near water. Livestock are also at risk from poisoning.
What should I do if I find blue-green algae?
Rivers users, particularly those with dogs, or those taking water for livestock or human consumption, should avoid contact with any thick dark brown-black algal mats (see photo), particularly those that are easily accessible, exposed on river edges or floating in shallow areas of riverbanks or near rocks. If blue-green algal mats are widespread in a river you should presume that the water may be unsafe for bathing or drinking.
Who should I call if I experience a reaction?
If you think you are experiencing a serious reaction, seek urgent medical attention. Advise your doctor of your potential exposure to toxic algae. Your GP has been asked to notify Regional Public Health or Wairarapa Public Health of any people with possible reactions.
Who should I call if I think my animal is sick?
If you are concerned about your animal(s), contact a vet immediately (the toxins can affect dogs within minutes). You or your vet can report any animal illness resulting from contact with the blue-green algae to your local council.
Who should I call if I think I’ve seen toxic blue-green algal mats?
If you see thick blue-green algal mats, please contact Greater Wellington on 04 384 5708 or your local council.