Waimea River toxicity warning
Alarming levels of potentially toxic algae found in the Waimea River at Appleby have prompted warnings.
The algae coverage has shot up from 15 to 60 per cent in a week, forcing the Tasman District Council to issue warnings to dog owners and people against going into the river.
The alert was raised yesterday after concentrations of the algae, cyanobacteria, were detected by the council on January 21.
Toxins produced by the algae have killed dogs and can make humans sick.
Owners should not let their dogs drink the water or scavenge near the water's edge in the lower Waimea River below River Rd down to the estuary, the council warned. While the algae is not always toxic the material in the Waimea River last year was linked to dog deaths and should be treated as toxic.
Blue-green algae, or cyanobacteria, forms thick, dark-brown mats in the river. The algae grows on the river's bottom from where it sloughed off earth-smelling mats on the riverbanks.
Lower levels (30 per cent coverage) of the algae have been found in the Waimea River at River Rd and 10 per cent coverage has been detected in the Motueka River at Alexander Bluff Bridge.
The council's communications manager, Chris Choat, said signs were in place but people needed to be aware of its potential presence in other parts of the Waimea and other rivers, not just in the sign posted areas, and take appropriate precautions.
To date, the toxic algae has not been observed in the Roding, Lee or Wairoa Rivers, he said.
Scientist Dr Susie Wood, of Cawthron Institute, said the appearance of the naturally occurring algae was "pretty standard" for this time of year when temperatures were warm and river levels low.
Regional research to date indicated changes in algae levels could be affected by the concentrations of nitrogen in the water, long periods of stable low river flows and possibly increases of sediment in the water which provided a food source for the algae.
Dr Wood said the algae in the Waimea River was mostly concentrated around the Appleby Bridge, where people visiting the river tended to stop.
She advised people to head to some of the region's other rivers, which were clear of the algae.
Mr Choat said people who have swallowed any of the algae should call their GP for advice. If dog owners believe their dog has been affected they need to ring their vet immediately.
The Nelson Mail