Water around the Grassy Narrows First Nation near Kenora, Ont., has been contaminated with mercury since a local paper mill dumped an estimated 10 tonnes of neurotoxins into the system between 1962 and 1970.
Grassy Narrows and the Wabaseemoong Independent Nations negotiated an out-of-court settlement with Ottawa, the province and two paper companies in the 1980s.
That included the creation of the Mercury Disability Board, which administers compensation for those whose health suffered as a result of mercury poisoning.
Grassy Narrows says it has now obtained a report commissioned by the board in 2009, but never publicly released, that found the government played down the scope of mercury poisoning and failed to provide adequate treatment for those affected.
The band is calling for the government to act on the report's findings and step up compensation and care.