Toxic algal mats in Masterton's Waipoua River

People should avoid contact with the Waipoua River at the Colombo Road bathing site in Masterton due to extensive cover of toxic algal mats in the river, Greater Wellington and Wairarapa Public Health warned today.

Masterton District Council is posting high risk warning signs at the site, advising people to avoid contact recreation and dog walking.  Checks at bathing sites further upstream are also being made and further signage may be posted.

Continuing warm and dry weather combined with low river flows has caused the mats to proliferate at this site and they have started to wash up on the river’s edge where they are easily accessible to dogs, stock and recreational users.

Toxic algae cover in other recreational rivers in the Wairarapa is currently low but is expected to increase in the coming weeks if the current stable weather pattern continues.  Council staff will continue to monitor the situation at selected bathing sites and website alerts and warning signs will be posted when appropriate.

Wairarapa Public Health advises everyone to avoid contact with toxic algae in rivers or on river edges and banks. 

Contact (skin contact, swallowing) can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects in humans. The toxins can be fatal to dogs and they are particularly at risk because they like to scavenge near water.

If any person or animal in your care exhibits signs of illness after being near the river/s, contact your doctor or vet immediately. 

For up-to-date information and warnings, visit www.gw.govt.nz/toxic-algae. If you see any toxic algal mats, contact Greater Wellington (06 378 2484) or an environmental health officer at your local council.

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 06 378 2484
or your local council.