Cyanobacteria mats found in Taranaki rivers posing health risks to swimmers

Taranaki Regional Council water quality scientist Angela Collins sampling for water quality.

Taranaki residents are urged to be cautious after potentially toxic cyanobacteria has been detected in four rivers.

Taranaki Regional Council staff have found mats of the blue-green algae in the Manganui, Waingongoro, Kaupokonui and Waiwhakaiho Rivers, raising health concerns for both swimmers and pets.

Cyanobacteria is a naturally occurring algae that often grows in rivers on rocks as thick brown or black mats. It has the potential to release toxins that can pose significant health risks to both humans and animals. When these mats become exposed on the edges of rivers, they can have a distinctive, unpleasant smell, often described as musty or swampy.

Water quality scientist Angela Collins said if people see the mats, it’s safest to stay out of the water.

“Children are at greater risk because their smaller body size means they need to ingest less toxin to become seriously ill, while dogs may be attracted to the musty smell.”

Mats of cyanobacteria have been found in four Taranaki rivers, with residents urged to avoid swimming if they spot the algae.

She said the cyanobacteria has been detected earlier in the season than usual.

“It is likely due to the drier winter we had – heavy rainfall and high water flow help to flush cyanobacteria.”

The council is closely monitoring cyanobacteria levels at selected rivers and lakes (where it is called planktonic) as part of its Can I Swim Here? programme, which began this week and runs through until March, said Collins.

“As we kick off the Can I Swim Here? programme, we want to remind the public of the risks posed by cyanobacteria and encourage everyone to be mindful when planning a swim – especially in the rivers where we’ve found the mats.”

Alongside cyanobacteria, water is tested for E. coli at freshwater sites and enterococci at coastal sites, both of which indicate possible faecal contamination.

She said any time water doesn’t look or smell right, it’s safest to stay out.

“If you come into contact with water contaminated with cyanobacteria, wash it off with clean water as soon as possible. If ingested, contaminated water may cause nausea, vomiting, diarrhoea, abdominal pain and, in more serious cases, liver or kidney damage. If you experience any of these symptoms, contact your doctor immediately.”