Water vapor is transparent. The coolness of the air causes the vapor to condensate into microscopic droplets of water that make up the mist and reflect sunlight. In the spring, the air is relatively warm and relatively little vapor is released from the water surface. No vapor will condensate above the water surface and hence no mist.

That doesn't mean there can't be mist in the spring. Air temperature and humidity vary a lot. The source of the condensating water is more likely to be a moist warm mass of air transported from afar cooling down over cold water.