"We sincerely apologise and take responsibility for the impacts of these discharges," Teck president and CEO Don Lindsay said in an open letter.

The company said the Crown would not proceed with charges relating to the same discharges from its Fording River and Greenhills steelmaking coal operations over the period from 2013 to 2019.

Environment and Climate Change Canada also recently issued a directive to Teck under the Fisheries Act, setting out additional measures to improve water quality and prevent calcite discharge. 

"Although there has been mining in the Elk Valley for more than 120 years, it was not until 2010-2012 - through independent research commissioned by Teck - that we began to understand the full extent of the impacts of selenium and calcite releases on water and aquatic health in the valley," Lindsay said.

He said the company had invested about $1 billion so far to implement the Elk Valley Water Quality Plan, which was developed in 2013 under direction from the provincial government and in consultation with the Ktunaxa Nation, scientists, and local communities.

Although there had been significant progress since 2012, there was much more to do and "no quick fixes," Lindsay said.

"We plan to further invest up to $655 million over the next four years alone on work to protect the watershed, with even more to come in the years ahead," he said.

"Along the way we have made progress and made mistakes, and we've learned from both, always striving to do better."

In a climate where ESG factors are increasingly prominent considerations for investors, Teck said earlier this month it was working to continually improve its sustainability performance as it released its 20th annual sustainability report.

Teck shares (TSX: TECK.B) have been on an upward trajectory since the COVID-19 sell-off of a year ago.

They closed up 5.6% on Friday to $23.95, capitalising it at $12.5 billion (US$9.9 billion).