Trout, like other fish, tend to eat less in the winter because their metabolism slows down in the cold water. However, they still need to eat to survive, and their diet in the winter typically consists of whatever food is available to them in the stream. In the winter, trout can be found feeding on aquatic insects such as midges, black flies, and stoneflies. They may also feed on other aquatic invertebrates like scuds, worms and leeches. If there is a significant population of these organisms in the water, the trout will feed on them.
Trout may also feed on small fish, such as minnows or sculpins, if they are present in the stream. Adjust your fishing techniques accordingly, try to fish after a series of warmer days, and fish mainly in the afternoons when the sun has had time to be on the water for a while.