The St. Lawrence Seaway closed its 2015 navigation season ice free on December 31st. Thirty-six million tonnes of cargo transited the waterway during the season, a drop of 9.5 per cent, compared with the 2014 volume of 39.9 million tonnes. Coal volumes were down by more than 40 per cent (to 2.5 million tonnes), while general cargo was down by 15.4 per cent (to 2.7 million tonnes). The largest commodity group, grains, was down by almost 11 per cent, to 10.8 million tonnes.

The 2015 season opened on April 2nd, about a week later than usual, reflecting the frigid conditions in early spring, and closed on December 31st with the passage of the vessel Mississagi through Welland Canal Lock 1 at 3:41 AM. The last vessel to exit the Montreal / Lake Ontario section was Baie St. Paul, which exited the St. Lambert Lock at 8:41 PM on December 30th.  The 2015 navigation season was 274 days in length.

The St. Lawrence Seaway Management Corporation announced 2016 wharfage and toll rate increases of 2 per cent.