The city pleaded guilty last week to violating the Fisheries Act.
More than three years ago a toxic product from the pulp-making process was spilled from the Watson Island pulp mill site into Porpoise Harbour.
An Environment Canada investigation found that the substance called weak black liquor is toxic to rainbow trout and charges were laid last December.
The agency says most of the penalty — $45,000 — is to be used to remove chemicals left in tanks or piping at the defunct mill site.
The Skeena Cellulose pulp mill was shuttered more than a decade ago, and the city ended up with the site in 2009 after it was seized from a Chinese-backed company for failing to pay municipal taxes.
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