Despite reservation cancellations and a drop in advance bookings caused by floods in Alberta, WestJet reported an eight per cent increase in passenger traffic for the month of June over the same period last year.

The Calgary-based airline's seat capacity also increased in that time — by a little more than 11 per cent — and that resulted in a drop in its load factor, which measures how full the airline's flights are overall.

The load factor for June was 76.8 per cent, compared to 79 per cent in June 2012.

Almost nine million people flew on Canada's second-largest airline since the start of the year, an increase of 5.7 per cent over the first six months of 2012.

"We continued to be pleased with our strong year-over-year traffic growth," said the airline's president and CEO, Gregg Saretsky.

But Walter Spracklin of RBC Capital Markets warned that the growth might not be enough to outpace the rise in capacity. The 8.3 per cent uptick in passenger traffic in June fell short of the analyst's forecast of 10 per cent.

"We are seeing the largest capacity uptick from WestJet since the first quarter of 2011, leading to what we believe will be continued pressure on yields and RASM (revenues per available seat mile)," Spracklin wrote in a report cited by The Canadian Press.

June also saw the launch of WestJet's regional carrier, WestJet Encore, with inaugural flights taking off June 24 from Calgary to four B.C. destinations and to Saskatoon. WestJet will add Brandon, Man., to Encore's serviced routes later this summer.

With files from The Canadian Press