The Wildlands League, a Canadian environmental group, is taking DeBeers to court for mercury pollution in the Attawapiskat River.
The province requires DeBeers to monitor any impact its diamond mine in the James Bay lowlands is having on local waters, but Anna Baggio, the Wildlands League's director of conservation planning, said the mining giant filed incomplete reports with the Ministry of the Environment between 2009 and 2016.
Baggio said some downstream tests show mercury levels are up since mining began.
"So that to me is a big alarm bell that we need to go, 'Whoa, what's going on here,'" Baggio said, "so that's why it's really important for this data to be transparent."
Baggio said by taking DeBeers to court she hopes to establish more clearly what the industry's role in protecting the environment should be.
"It's very important that we set a precedent here and that we hold industry to account, because we definitely need the monitoring program to have integrity," Baggio said.
Both DeBeers and the Ministry of Environment declined interviews, saying they take these concerns and their responsibilities seriously.
The Attawapiskat First Nation also declined an interview, saying it was surprised the Wildlands League is taking legal action without consulting the community.