It took 15 minutes for the play date to turn deadly.
Melissa Martin and Denise Mintz's three dogs - Abby, Izzy and Harpo - had spent last Thursday evening romping in the mud and chasing their ball at a pond in Wilmington, North Carolina. The evening getaway was a welcome reprieve from the late-summer heat.
But unbeknownst to the dogs and their owners, the relentless sun had also made the pond a bathtub of toxins. A poisonous microscopic bacteria called blue-green algae had grown in the water, a threat Martin and Mintz did not know about until it was too late.
On their way home, Abby, a white West Highland terrier, fell first and began to seize, Martin told CNN. They rushed to the veterinary hospital, where Izzy, also a Westie, began seizing as well. Six-year-old Harpo, a doodle mix who worked as a therapy dog for hospital patients, fell ill too.
By midnight, Martin told CNN, all three dogs were dead.
"We are gutted," Martin wrote on Facebook soon after. "I wish I could do today over. I would give anything to have one more day with them."
Since then, another family has made headlines for the loss of their border collie, Arya, who died from what their vet suspected was blue-algae poisoning after swimming in a Georgia lake. And in Austin, Texas, in early August, three dogs died because of the same neurotoxins, their owners said, and the city closed the lake where the dogs had been swimming.
Martin told CNN she now hopes to help prevent more dog deaths by educating pet owners about the deadly algae blooms and advocating for warning signs near ponds, lakes and canals where the toxins have taken over.
"I will not stop until I make positive change," she told CNN. "I will not lose my dogs for nothing."
As of Monday morning, a Go Fund Me page had raised more than $3,000 to help Martin complete her mission.
"I can promise you every penny raised will be used to raise awareness and get signs and information out," Martin wrote on Facebook.
Dangerous algal blooms are a "major environmental problem" in all 50 states that scientists believe will continue to wreak havoc on U.S. waterways with the rising threat of climate change, according to the Environmental Protection Agency. Red tide algal blooms have killed marine life on the Florida and Mississippi coasts.
Toxic algae can affect the nervous system, liver and kidneys in humans and animals, though children and dogs are most susceptible because they tend to wade in shallow areas on the edge of ponds or lakes where the algal blooms are concentrated, according to the North Carolina Department of Health and Human Services. It can be especially dangerous for dogs, who drink the water or ingest the blooms by licking themselves.
To thrive, algal blooms need sunlight and stagnant, nutrient-rich water, which is most common in lakes, ponds and canals but can also be present along the coasts of bays, gulfs and oceans.
When water is slow-flowing, it warms faster - allowing toxic bacteria to thrive and the algae to grow faster and thicker. Additionally, algal blooms absorb sunlight which warms the water further.
Other issues related to climate change affect algal blooms, including salinity changes from droughts, higher levels of carbon dioxide, extreme rainfall that promotes runoff of man-made toxins and sea level rise that causes warm shallow waters, according to the EPA.
Humans contribute to inserting more nitrogen and phosphorous into U.S. waterways, which creates the nutrient-rich environment in which algae thrives. Storm and wastewater, fossil fuels, agricultural runoff from crops and livestock and home fertilizer can drain into streams and soak into groundwater, according to EPA.
Martin told local TV station WECT that they would have never taken their dogs into the water if they had known about the dangers.
"I want to see signs on every body of water like this," Martin told the TV station. "I don't care if it says private property or no trespassing or whatever. Put some signs up so people know."
All three of their dogs were therapy certified, Martin and Mintz told WECT, and their doodle mix Harpo had earned local fame in 2014 when Martin and the dog asked residents in North Carolina to "adopt" people living in senior facilities during the holidays. The "Harpo Saves Christmas" initiative brought sponsors to all 171 residents of a facility, and Martin and Harpo delivered their gifts on Christmas eve.
In her Facebook post and in her interview with WECT, Martin said she had been writing a book about Harpo's work as a therapy dog, with the goal of getting her pup on "Good Morning America" or the "Ellen" show.
"I was trying to finish this book before he got too old to do any of that," Martin told WECT. "Now he's already gone, so I have to do it for him and not with him."
Their awareness campaign, Mintz told the TV station, will honor their "three pups' legacy."
"If we can touch anybody, if we can help anybody not have to go through what we are right now, we will have done our part," Mintz said.