The fumes, caused by what authorities called "a chlorine incident", forced the evacuation of the complex in this central Interior community and sent 70 people to hospital, the majority of them children.
"People just said 'you've got to get out," said Abbi Taylor, a 17-year-old swim coach who was there.
She said the kids, who were mostly under the age of 12, were in the pool at the time, warming up for the meet. A hockey game was also going on in the complex.
Taylor said a "wall of people" began running towards the door after the alert was given.
The children, many still wearing wet bathing suits, were ushered to the adjacent ice arena before the whole building was evacuated and ambulances arrived.
"It was pretty scary seeing, like, eight-year-olds with oxygen masks on and stuff," Taylor said. "It was scary."
Taylor is so used to smelling chlorine that she at first didn't think the chemical was the problem.
"But then it started to smell a lot, and a lot and a lot. And I was like, 'It kind of smelled weird.' But I just didn't really think too much about it."
Meantime, pool staff trying to solve the problem were coughing and lifeguards were trying to keep people calm, she said.
Soon, 70 people were on their way by ambulances and private vehicles to Cariboo Memorial Hospital, said health-services administrator Allison Ruault.
In total, 45 children and 25 adults were treated, she said, and all but two people -- one adult from Williams Lake and a child -- have been released.
Angela Swyers, a resident of Quesnel, B.C., said the child is her son, eight-year-old Billy Swyers.
"He's showing signs in his lungs that the doctors aren't happy with," she said. "So just as a precaution, they are keeping him overnight, giving him some antibiotics, and making sure he's OK before they send him home."
Chlorine is used to sanitize pool water, but in high concentrations, particularly once it's airborne, the gas can turn toxic. Some of the symptoms include a burning sensation in the eyes and mouth and difficulty with breathing.
Dr. Sydney van Wyk, chief of staff at the hospital, said the two who were hospitalized are stable.
Wyk said chlorine gas is problematic because it dissolves into the moisture found in the upper and lower airways and forms an acidic compound that irritates the lung tissue and causes swelling.
He said the irritation and swelling can give patients asthma and bronchitis-like symptoms, like wheezing, coughing and shortness of breath and sometimes chest pain.
In some individuals, it can also result in bacterial pneumonia, he added.
"If someone gets worse or fails to improve over the next couple of days, you definitely want to seek medical attention and exclude any complication," he said.
Swyers said she and Billy were sitting on the bleachers when she began to smell fumes in the air and everybody ran out of the pool.
Many of the children were coughing heavily, she added.
At the hospital, Billy was placed on a ventilator and given medication, she said, noting doctors also performed blood work and an X-ray.
"I just want to make sure he's better," said the boy's mother. "So we'll do whatever we can to get him healthy and then go home."
Kathie Kovacs, a resident of Quesnel, said she wasn't at the competition but drove to Williams Lake, a distance of about 124 kilometres, after she learned her 12-year-old daughter, Janna, had been taken to hospital.
"When she coughs it sounds like almost like a seal barking. It's a really, deep horrible cough, actually," said Kovacs.
Janna ran out of the pool after she thought somebody had "puked," said Kovacs, noting some parents have told her a smaller, shallower pool at the facility had been drained.
Initially, Janna was taken to hospital by ambulance and released, but she had to be taken back a second time, said Kovacs, noting her husband was also treated.
Investigators don't know what caused "the chlorine incident", but city spokesman Ken MacInnis said the pool uses chlorine gas, not liquid chlorine, and dispenses it by computer.
Ruault said the day proved to be busy for the hospital, which is usually staffed by two nurses and a doctor on a Sunday.
"Typically in a day, in a 24 hour period, we would see 50 to 60 people," she added, noting the hospital had to call in extra staff to deal with the influx of patients.
"In that roughly three-hour period we saw more than we would see in a 24-hour period."
-By Keven Drews in Vancouver