Lake warnings for toxic algal blooms

Warnings in place - 1 May 2012

New toxin-producing algal species found in the Groynes

Issued: 1 October 2010

Background

As part of ongoing research into toxin production in freshwater algae, Francine Smith, a University of Canterbury PhD student, in May 2010 identified the presence of a toxin in the blue-green alga Scytonema in lakes of the Groynes recreational reserve. Scytonema produces a neurotoxin known as paralytic shellfish poison, which is more commonly associated with harmful algal blooms in the marine environment.

Scytonema is dark-green in colour and forms mat-like growths amongst other aquatic plants and on stones along the edges of lakes and ponds. Expert advice suggests that Scytonema is native and widespread in New Zealand, although no comprehensive surveys have been conducted on its distribution. Environment Canterbury-supported surveys into its distribution in Canterbury are planned for October 2010.

Photo provided by Francine Smith

What is the risk of exposure to the toxin?

Unlike other freshwater blue-green algae such as Phormidium, which are problematic during warmer summer months, Scytonema is found year-round at the Groynes.

The neurotoxin was detected inside the cells of Scytonema but not in samples collected from the water column. Environment Canterbury advises that humans and animals should avoid contact with water or algal/plant debris at the Groynes lakes. Possible symptoms of toxin exposure include skin rashes, nausea, tummy upset and tingling or numbness around the mouth or tips of fingers. If you experience any of these symptoms after contact with water, please visit a doctor immediately and contact Environment Canterbury.

Is it safe to boat and kayak at the Groynes?

Although the toxin has not yet been detected in water column samples, direct contact of water with the skin should be avoided if possible.

Is it safe to eat fish at the Groynes?

Experts agree that there is a very low risk of toxin accumulation in the flesh of fish. This is supported by results from analyses of the flesh of trout collected from the Groynes, where no neurotoxin was detected. However, Environment Canterbury recommends that the internal organs of any fish caught at the Groynes for consumption are discarded.

The annual “Take a kid fishing day at the Groynes”, organised by Fish and Game New Zealand, will take place on Sunday 17 October 2010. For more information see the following link: http://www.fishandgame.org.nz/Site/Regions/NorthCanterbury/KidFishing.aspx

Many fish caught during this event are eaten. However, because large numbers of hatchery reared salmon and trout are stocked in the Groynes lakes on the day prior to the event, the consumption of these fish should pose no risk of toxin exposure.

Is the occurrence of Scytonema linked to land-use effects?

It is currently unknown what factors are associated with the growth and occurrence of Scytonema. Environment Canterbury will be conducting a survey into the distribution of Scytonema to gain a better understanding of the species ecology.

General advice on lake algal blooms

If there is a health warning in place:

Never swim or take part in any activity that may result in accidental consumption or exposure to water affected by algal blooms if a health warning is in place for that area, even if there are no visible signs of a bloom. Do not let stock or dogs swim or drink from the water.

If a health warning is in place, it means that cyanobacteria (blue-green algae) are present in large numbers in that bay/lake. Cyanobacteria are capable of producing toxins that are harmful to humans and animals if swallowed or if exposed to skin (such as may occur when swimming, skiing or kayaking etc).

If there is no health warning in place:

Wind blowing onto shore may concentrate a bloom in a bay and make it unsafe for recreational contact. This can occur at any time of the year, but is more common in warm summer months. Hence, even if no warnings are in place for a lake or bay, you should still assess the situation carefully before entering the water.

Caution: If the water is cloudy, discoloured, or has small globules suspended in it, it is better to be cautious and totally avoid that lake or bay.

Even if the water appears completely normal to the naked eye, it can still have large numbers of algae present. If you experience health symptoms (such as those described below) that come on within minutes of contact with the water, you should avoid further contact with the water and, if symptoms persist, contact Community and Public Health 03 379 9480 or see your doctor.

Cyanotoxin health symptoms

Swimmers have been known to develop adverse reactions after bathing and showering in water containing blue-green algal blooms. These include allergic reactions, asthma, eye irritations, rashes and blistering around the mouth and nose, gastrointestinal disorders (abdominal pain, cramps, diarrhoea). Some of these can be caused by the mere presence of large numbers of algal cells in the water, but some symptoms are related to the release of toxins by the bloom. These toxins are colourless and odourless. They are unaffected by boiling the water and can persist in the water after the bloom has subsided. They can also be released at any stage of a bloom and may or may not be localised in a bay.

Identify toxic algal bloom