Why can wind prevent a large lake from developing a stable ice cover?

Wind prevents a large lake from developing a stable ice cover primarily by maintaining mechanical mixing that disrupts the formation of a continuous ice sheet.12

Under calm conditions, water cools until it reaches the freezing point, allowing a stable layer of ice to form at the surface. However, in large, unprotected lakes, wind stress creates turbulence that mixes the water column. This process overcomes the natural tendency of water to form a stable, less-dense layer at the surface as it cools below 4° C (39° F).21

Because the wind continually agitates the surface, any initial ice crystals are mixed into the water or broken apart. While this may lead to the formation of small ice floes, the wind prevents these from freezing together into a solid, stable cover until the ice grows thick enough to withstand the wind's force. In some large lakes, such as Lake Erie, these wind effects are so significant that a stable ice cover may rarely form over the entire surface.12