First Nations leaders are mourning the death of a former Ontario chief.

Ontario Regional Chief RoseAnne Archibald says the Chiefs of Ontario are extending their deepest condolences to the family and friends of former Grassy Narrows chief Simon Fobister.

Archibald says Fobister was a strong and outspoken leader for the northern Ontario community, adding he played an instrumental role in advocating for proper health care for a community that has been beset by the impacts of mercury posioning.

Fobister fought to convince the federal government to build a treatment centre in Grassy Narrows, arguing it was critical for them to get the medical help they need closer to home.

The facility has not been built yet but the office of Indigenous Services Minister Seamus O'Regan says it remains steadfast in its commitment to proceed with the project.

Assembly of First Nations National Chief Perry Bellegarde also expressed his condolences, calling Fobister an advocate for the health of his people, their traditional territories and the rights of all First Nations.