Health warnings

For cyanobacteria, avoid water that is cloudy, discoloured, musty smelling, or has small globules, coloured scrum or thick dark brown/black mats on the bed of the river, with a slimy velvety texture.

• Read more on keeping dogs safe from cyanobacteria (PDF File, 237.57KB).
• For faecal contamination, check what to look out for on LAWA’s website.

Cyanobacteria are an ancient group of organisms with characteristics in common with both bacteria and algae.

The naturally occurring cyanobacteria are widespread in many lakes and rivers in New Zealand.

Under favourable conditions, cyanobacteria cells can multiply and form suspended planktonic blooms in slow-moving water such as lakes, or thick mats attached to benthic substrates such as rocks in river beds.

Some cyanobacteria species have the ability to produce natural toxins called cyanotoxins, which are potentially harmful to people and animals. If potentially toxic cyanobacteria are abundant, you should presume that the water is unsafe for contact recreation or consumption.

Types of cyanobacteria

While planktonic (suspended) and benthic (stream bed) cyanobacteria share similar traits, their visual appearances are quite different. 

Planktonic cyanobacteria blooms are not confined to lakes nor are benthic mats confined to rivers, but this is where we most often see them.

Planktonic cyanobacteria in lakes

Planktonic cyanobacteria are algae that suspend in the water column of slow moving waters such as a lake. The species that cause toxic blooms are Nodularia, Anabaena, Microcystis and Picocyanobacteria.

Nodularia, Anabaena and Microcystis generally form a thick, bright green colouration to water and can produce scums on the water surface.

Picocyanobacteria, which is a major species causing potentially toxic blooms in Te Waihora/Lake Ellesmere, often do not have obvious visual traits.

Benthic cyanobacteria in rivers

Benthic cyanobacteria is attached to substrates such as gravels, cobbles and boulders on a river bed. Its appearance depends on species. Phormidium occurs naturally throughout Canterbury and in flowing water can form thick, dark brown/black cohesive mats. The species may detach from the riverbed and become caught in other debris in the river.

When Phormidium mats die and dry out, they become light brown or white in colour, but may still be toxic. Nostoc is another mat-forming benthic cyanobacteria. It forms small globular mats or gelatinous ‘bobbles’ firmly attached to hard substrates and is relatively translucent in colour. 

The more brightly-coloured long filamentous green algae that are commonly found in rivers and streams are harmless as they do not produce toxins.

For more information download our cyanobacteria factsheet (PDF File, 907.85KB).

Blooms form when cyanobacteria start to multiply very quickly, usually due to changes in environmental conditions such as warm temperatures, sunlight, low or stable river flows, and high levels of nutrients.

In rivers – how to spot cyanobacteria

This cyanobacteria (called benthic cyanobacteria) grows on the bottom of river beds.

It appears as thick dark brown or black mats that have a slimy or velvety texture and musty smell.

In lakes, ponds and lagoons – how to spot cyanobacteria

This cyanobacteria (called planktonic cyanobacteria) is suspended in the water. Water can look cloudy, discoloured, or like it has small globules in it. Planktonic cyanobacteria may not have obvious visual traits.

Watch this video on how to identify potentially toxic cyanobacteria.

Symptoms of cyanobacteria poisoning can occur within 30minutes, including:

For people

• tingling or numbness around the fingertips and/or mouth
• breathing difficulties
• gastrointestinal symptoms
• skin rashes

For pets and livestock

• panting
• lethargy
• muscle tremors
• twitching
• convulsions

E. coli

Gastroenteritis, but respiratory illness and ear/skin infections may also occur.

Read more about the health risks associated with contaminated water.

Read MPI’s guidance on shellfish collection and consumption from areas where warnings have been issued.

If you are in any doubt about the water quality, then keep your dog on a leash and away from the water.

If symptoms appear after being in contact with a waterway, contact your doctor or a veterinarian immediately.

You, your doctor, or your veterinarian can report potentially toxic cyanobacteria blooms to Environment Canterbury at any time by calling 0800 324 636 or going online to www.ecan.govt.nz/contact

• Find out more on how you can keep your dog safe this summer.

Water containing micro-organisms, chemicals, phytoplankton or cyanobacteria can pose a risk to health through recreational contact, drinking and gathering mahinga kai.

Find out more on mahinga kai and health warnings.

Monitoring of ‘faecal indicator bacteria’ (including E. coli) is vital. ‘Indicator bacteria’ signal the levels of disease-causing organisms present in the water.

It’s important to test for these in water used for recreational activities as they can pose a health risk.

The most common illness they cause is gastroenteritis, but respiratory illness and ear/skin infections may also occur.

Find out more about health risks associated with contaminated water.

Find out what you can do to keep our lakes clean this summer