LAC SAINTE ANNE -- Pope Francis prayed for healing Tuesday from the "terrible effects of colonization" as he led a pilgrimage to a Canadian lake that has been known to Indigenous people for centuries as a sacred place of healing.

The prayer service at Lac Sainte Anne in Alberta was one of the spiritual highlights of the pontiff's six-day visit to Canada to atone for the Catholic Church's role in running residential schools that forcibly assimilated the country's Indigenous children into Christian society. On Monday he apologized for the "catastrophic" ways families were torn apart; the following day he transitioned to praying to help them heal from the "wounds of violence."

"In this blessed place, where harmony and peace reign, we present to you the disharmony of our experiences, the terrible effects of colonization, the indelible pain of so many families, grandparents and children," Francis said on the shore of the lake. "Help us to be healed of our wounds."

The ceremony fell on the Feast of St. Anne, the grandmother of Jesus and a figure of particular devotion for Indigenous Catholics, who every year make pilgrimages to Lac Sainte Anne to wade into its waters. Francis highlighted the importance grandmothers have in Indigenous families, and recalled the critical role his own grandmother Rosa had in transmitting the faith to him as a youngster in Buenos Aires, Argentina.

"Part of the painful legacy we are now confronting stems from the fact that Indigenous grandmothers were prevented from passing on the faith in their own language and culture," he said.

More than 150,000 Indigenous children in Canada were taken from their homes and made to attend government-funded Christian schools from the 19th century until the 1970s in an effort to isolate them from the influence of their families and culture. The aim was to Christianize and assimilate them into mainstream society, which previous Canadian governments considered superior.

In his first event in Canada, Francis blasted the residential schools Monday as a "disastrous error" and apologized at the site of a former school in Maskwacis for the "evil committed by so many Christians against the Indigenous Peoples."

Emotions were still raw a day later as those words were digested and dissected.

Murray Sinclair, the First Nations chairman of Canada's Truth and Reconciliation Commission, welcomed the apology but said Tuesday that it didn't go far enough in acknowledging institutional blame for the papacy's own role in justifying European colonial expansion and the hierarchy's endorsement of Canada's assimilation policy.

"It is important to underscore that the church was not just an agent of the state, nor simply a participant in government policy, but was a lead co-author of the darkest chapters in the history of this land," Sinclair said in a statement.

Sinclair said church decrees led directly to the "cultural genocide" of Indigenous people by underpinning colonial policy and the Doctrine of Discovery, a 19th-century international legal concept has been understood to justify colonial seizure of land and resources by European powers.

Trip organizers pushed back on his criticism, insisting that Francis had indeed "accepted full responsibility for the Catholic Church's role in the residential school system."

"His decision to apologize on Canadian soil, in a year where he faces significant health challenges and has had to cancel other international travel, demonstrates his understanding of the Catholic Church's institutional responsibility to contribute to the reconciliation journey," Neil MacCarthy, communications chief for the papal visit, told The Associated Press via email.

He added that Canada's Catholic bishops were working with the Vatican on issuing a new statement on the papal bulls associated with the Doctrine of Discovery, even though the Holy See has already said the decrees have no legal or moral authority in the church today.

"We understand the desire to name these texts, acknowledge their impact and renounce the concepts associated with them," MacCarthy said.

Gerald Antoine, Dene national and Assembly of First Nations regional chief, said he had hoped the pope might renounce the decrees while in Canada but he was grateful for the attention the visit and apology have brought to a history that his own family experienced.

"The world is seeing we are telling the truth," Antoine said. "Our family got uprooted, displaced and relocated. This is what our people have been saying. Nobody ever cared to listen."

Francis didn't dwell on the apology or the church's fraught history during a morning Mass in Edmonton's Commonwealth Stadium dedicated to St. Anne and grandparents, which drew some 50,000 people. Due to knee problems, the 85-year-old pontiff celebrated the Mass from a seated position behind the altar.

"Thanks to our grandparents, we received a caress from the history that preceded us: We learned that goodness, tender love and wisdom are the solid roots of humanity," Francis said. "We are children because we are grandchildren."

He later carried the grandparental theme to Lac Sainte Anne, where an estimated 10,000 pilgrims gathered at and around the shores of the lake amid vast acres of bright yellow canola flowers that bloom at the peak of summer. Some travelled from faraway parts of Canada to participate in the pilgrimage, which was restarting after two years of COVID-19 closures.

"I am happy he apologized," said Myles Wood, who came from Saint Theresa Point in remote northern Manitoba with his wife, mother and members of their parish. "I've got a lump in my throat," he said after Francis passed by and blessed the crowd with holy water from the lake.

Francis arrived to the sound of drums and ululating and paused for a minute of prayer at the water's edge. Ahead of the visit, Alberta health authorities issued a blue-green algae bloom advisory for the lake, warning visitors to avoid contact with the blooms and refrain from wading where they are visible.

The lake is known as Wakamne, or "God's Lake," by the Alexis Nakota Sioux Nation who live nearby, and Manito Sahkahiga, or "Spirit Lake," by the Cree. The name "Lac Sainte Anne" was given to it by the Rev. Jean-Baptiste Thibault, the first Catholic priest to establish a mission on the site.

For Lorna Lindley, a survivor of the Kamloops residential school in British Columbia, where the first presumed unmarked graves were discovered last year, the day was difficult. She attended the morning Mass to honour her late parents, who were taken to a residential school at age 5 in a cattle truck.

"For myself it's really heavy," Lindley said. "It's hard. No matter how many times you apologize, it doesn't take away the hurt and pain."

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If you are a former residential school survivor in distress, or have been affected by the residential school system and need help, you can contact the 24-hour Indian Residential Schools Crisis Line: 1-866-925-4419

Additional mental-health support and resources for Indigenous people are available here.