Tucker died within two hours of swimming at the Waimakariri River this month.
Haslett, who lives in West Melton, said the gregarious, energetic 11-month-old was swimming and fetching sticks, while his more placid sister Tess mostly looked on from the riverbank.
Haslett’s partner Paul Foster had taken the pair to the river, about 2km upstream of the popular Willows spot which has a dog park.
But within half an hour after arriving home, Tucker had diarrhoea and was suffering seizures.
As she and Foster drove him to a vet in Christchurch, Tucker became unresponsive. He was pronounced dead on arrival.
An autopsy was not conducted and the cause of death is not confirmed, however, the vet suspected poisoning from cyanobacteria.
This type of algae is a well known toxin to dogs. It appears in rivers as thick dark brown or black mats that have a slimy or velvety texture and musty smell.
Haslett suspected the cyanobacteria may have been in unseen quantities in the water and accidentally swallowed by Tucker.
She believed the low river levels at the time probably enhanced concentrations.
She wanted to share her story to warn other dog owners. She and Foster would not be taking Tess to the rivers again in summer.
"I would hate for somebody else to go through it, it’s absolutely horrific," Haslett said.
"Tucker was like the life of the family. He was a talker, very playful, lots of people in the community knew him."
Environment Canterbury science team leader – surface water science Shirley Hayward said river health warnings were issued based on human health, not dog health.
"We’ve monitored multiple sites across the Waimakariri River. All sites show low levels of cyanobacteria, well below guideline values for human health associated with swimming,” Hayward said.
"It is important for dog owners to know how to identify potentially toxic cyanobacteria in rivers, to prevent their dogs from getting sick."
Community and Public Health has issued a health warning for the Selwyn River, from Whitecliffs Domain down past Glentunnel camping ground, due to moderate to high cyanobacteria cover in the area. There are also warning at the Rakahuri/Ashley River at the Rangiora-Loburn Bridge and Whakatipu/Twizel River at picnic area upstream of State Highway 8.
After Sunday's fire at the Sutton Tools manufacturing plant in Kaiapoi a warning about toxic oil has been issued for the Cam/Ruataniwha River. Oil has been detected in the Kaiapoi and Waimakariri rivers downstream of where it meets the sea.
Freshwater scientist Susie Wood told Radio New Zealand she estimated there had been more than 200 dog deaths across the country in the last 10 years from dogs eating or licking algal mats in rivers. She said climate change and nutrients and sediments entering rivers were contributing factors to growing algae levels.
Canterbury Medical Officer of Health Dr Cheryl Brunton said there were two cases of cyanotoxin poisoning in humans reported to the Canterbury District Health Board in the last five years.
Late last year a child developed a skin rash after playing in water at Chamberlains Ford on the Selwyn River. The first case was in 2020, and involved an individual who presented with tingling hands and feet and stomach cramps after exposure.
