Thousands of Catholics converge on the lake west of Edmonton each year, where bathing in the water is a central part of the experience.
People believe water in Lac Ste. Anne has the power to heal and many were undaunted by the advisory, issued Tuesday by Alberta Health Services.
"Tell you the truth, I believe in miracles," said Marianne Guetre. "I believe in this water, I trust it."
However, Alberta Health Services is warning people to stay out of the lake and not drink the water because blue-green algae produces a toxin that can cause a range of symptoms to those who come in contact with it.
"They can vary from relatively minor things like skin irritation or throat irritation, to more serious problems, like if people, for example, ingest this toxin on an ongoing basis they can develop liver problems," said Dr. Gerry Predy, senior medical officer of health for Alberta Health Services.
Predy admits that health officials weren't aware the pilgrimage was on when they first issued the advisory. He said that staff were directed to contact organizers as soon as they found out.
Father Garry Laboucane believes AHS should have made a greater effort to notify them sooner.
"They should have been more proactive, in my judgement," he said. "More proactive about contacting the police or coming out here because I don't have email here, and I don't read the paper, I don't have the radio on. How do we know?"
Although signs were up around the site on Wednesday, many pilgrims didn't know about the advisory or decided to go in anyway.
"The water is healing. I know it is," said Loretta Belcourt. "My daughter — the doctors had said she'd live till she's 14 and she's 38 now and she's been coming since she was three years old."
Organizers said they've had no reports of anyone getting a rash or becoming sick after contact with the water.