Supreme Court Justice Ted Richard found BHP not guilty on charges under the federal Fisheries Act. The company faced a maximum fine of $1 million on each of four counts.

"The Crown has proven beyond a reasonable doubt that the accused corporation did indeed deposit a deleterious substance, sediment, in waters frequented by fish," said Richard, who added that BHP's actions were permitted under a Jan. 7, 1997 authorization from the Department of Fisheries and Oceans.

Richard released a 49-page decision on the matter, which was argued during a 10-week trial that saw 26 witnesses take the stand and lawyers present 250 exhibits.

"We're very pleased, of course," said Ekati president and chief operating officer Jim Excell. "Coming off with a not guilty is a very good decision from our point of view, because we believe that was the case. And we're glad to see the court has supported that."

"The Crown is satisfied that there was a fair hearing of the evidence," said Crown Prosecutor Ari Slatkoff. "(But) we're disappointed that the court did not agree with the Crown's submissions."

Prosecutors argued that an unauthorized extension to a drainage ditch at the Ekati site in 1997 clouded Kodiak, Moose and Little Lakes with 18,000 cubic metres of sediment.

Despite the win for BHP, Slatkoff said he was happy the court sided with the prosecution on one issue: the applicability of the Fisheries Act to lakes around Ekati.

BHP argued that the lakes were so small and remote from human habitation that the Fisheries Act did not apply. Prosecutors countered that with fish tagging studies that showed the lakes were part of a larger system feeding Lac de Gras.

That means, said Slatkoff, that "you still need authorization by the Department of Fisheries and Oceans to destroy those lakes."

Excell said the decision won't impact operations at Ekati.

"Remember, you're talking about an event that occurred five and a half years ago," he said. "It was certainly a regrettable event, but at the same time have our systems in place."

The Crown has 60 days to appeal the decision. Slatkoff said Monday it was too early to tell if the prosecution will appeal.