The motorcycle officer was following an anti-pipeline demonstration through the city.
Police say he was knocked off his motorcycle by a driver who made a U-turn into his path.
The officer requires surgery to repair a fractured knee.
The driver is co-operating with investigators.
First Nations groups organized a rally Sunday protesting the proposed Enbridge pipeline that would transfer Albertan oil to Kitimat ports.
The federal government is expected to announce its final decision on the $7 billion pipeline project in the coming days, with many expecting Ottawa to give it the go-ahead.