Long hot spell raises algae alarm

Hawke's Bay Regional Council is advising people to take care around lakes, rivers and streams because of the increasing likelihood of algal bloom. Photo / File

Current weather - resulting in lower river flows and warmer water temperatures - will increase the likelihood of algal blooms in Hawke's Bay fresh waterways, the Hawke's Bay Regional Council says.

The Hawke's Bay Regional Council and Hawke's Bay District Health Board are reminding people to take care around streams, rivers and lakes as algal blooms can be toxic to humans and dogs.

HBRC staff have not observed any cyanobacteria mats yet this summer but are monitoring popular recreational sites on the Ngaruroro, Tutaekuri and Tukituki Rivers each week.

Stephen Swabey, the council's science manager said: "Algal blooms occur in many of our rivers and lakes when summer temperatures go up and there's less rainfall, and when you are around a waterway, just be aware of the water quality as some blooms can be hazardous to your health or your animals."

Cyanobacteria are single-celled organisms that naturally occur in water environments, but in warm nutrient-rich conditions cyanobacteria cells can multiply quickly to form algal blooms. Large numbers of cyanobacteria can also grow as mats on river and lake beds which can then detach and float to the surface.

In previous summers cyanobacteria mats have been found in Hawke's Bay's shallow braided rivers. The mats are identifiable by a strong musty smell and can vary in colour from brown/black when in the water to a pale brown/whitish colour when dry.

Some cyanobacteria species produce toxins (cyanotoxins), which pose a risk to humans and animals when consumed or by direct contact during recreational activities. River users should avoid any contact with algal mats, avoid swimming in water where the mats are present, and keep dogs from scavenging around the river.

Hawke's Bay District Health Board Medical Officer of Health, Dr Lester Calder, said: "Contact with the toxic form of the mat may cause vomiting, diarrhoea, skin rashes and numbness or tingling around the mouth."

He also warned pet owners that dogs were particularly susceptible to the toxins with paralysis a possible outcome.

Anyone displaying signs of illness after being in a riverbed should seek medical advice from a doctor immediately.

Similarly, dogs or other animals that get sick after being in a river should get prompt veterinary attention.

The HBDHB Public Health Unit should be alerted in the event of health issues occurring after contact with river or lake water. The On Call Health Protection Officer can be contacted on 06 834 1815.

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