The City of Thunder Bay is investigating what exactly caused the opening of the Boulevard Lake dam on Sunday night, draining the north-side lake. The lake levels were reported as normal at 10 p.m. Sunday, according to city engineering and operations director Kayla Dixon, who spoke at a media conference held at the lake on Monday afternoon. However, at some point after that, 11 of the dam's 12 gates were opened, mostly draining the lake overnight. The city was notified of the low water levels at about 7 a.m. Monday, but officials don't yet know exactly why the dam was opened.