Norellco Contractors Ltd. admits it spilled 34,000 litres of chlorinated water in June and July of 2012 into the river in St. Albert, just north of Edmonton.
The company was ordered to pay the cash after pleading guilty in provincial court to an offence under the federal Fisheries Act.
Chlorine is highly toxic to fish.
The Sturgeon River, which flows into the North Saskatchewan River, is home to fish species including white sucker, northern pike and longnose dace.
Environment Canada says the spills happened within a week of each other on the same high-pressure water main, and the breaches of the line were only metres apart.