Like Terry mentioned, Walleye on Lake O are closed Feb and March...their typical spawning period. Here's an excerpt from the Govt of Canada's site....
"Normally, spawning begins shortly after ice breaks up in a lake, at temperatures of 7° to 9°C but has been known to occur over a range of from 6° to 11 °C.
Courtship may commence much earlier when water temperature is at 1°C. The males move to the spawning grounds first. These are usually rocky areas in flowing water below impassible falls and dams in rivers and streams, coarse-gravel shoals, or along rubble shores of lakes at depths of less than 2 m. "
As you can see...for Lake Ontario, this would correspond to the Feb/March time period. Feb for courtship and March for spawning.