The Otago Regional Council (ORC) is reminding people across the region to be on the lookout for toxic algae following two confirmed toxic algal blooms last week.

ORC lakes scientist Hugo Borges said ingesting these algae, which were found in Waianakarua River and Butcher’s Dam, could make humans and pets sick.

“This can happen anywhere in the region, and while ORC staff look out for algae during the weekly water quality checks in summer, we can’t cover every waterway in Otago all of the time,” he said.

In lakes and ponds toxic algae looks like pea soup, and in rivers it looks like black-brown tar on rocks and in mats on the riverside, he said.

Toxic algae, or cyanobacteria, thrive in warm, nutrient-rich conditions and when river flows are lower than normal.

A toxic algal mat on a rock from a river.

For most of the year, these algae are present in smaller amounts, and it’s only in the right conditions that they bloom and can cause issues, Hugo said. 

“Our best advice is for people to learn how to recognise these algae and practice caution around lakes and rivers in summer. If in doubt, stay out.” 

If ingested, toxic algae can cause significant illness and can be fatal for dogs, who can be particularly attracted to the smell of algal mats from rivers.

“That’s why it’s important for people to learn how to identify toxic algae, stay vigilant, and report sightings of potentially toxic algae to ORC.”

Anyone experiencing a reaction from contact with toxic algae should seek urgent medical attention, and any signs that a dog may have consumed toxic algae, such as lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsion, should be treated as an emergency and referred to a vet immediately.

To learn more about potentially toxic algae, including how to identify algal blooms in rivers and lakes, see this LAWA factsheet.

To report algal blooms in Otago lakes and rivers, contact the pollution hotline: 0800 800 033.

PHOTOS: Supplied