Lake Michigan is the only Great Lake that sits entirely within the United States. Menu Compartments White oak (Quercus alba) The white oak, Illinois' state tree, is a flowering angiosperm that can grow to be 100 feet tall, three feet wide, and can live to be 400 years old! Decomposers are the living/biotic beings which occupy the last stage of the food chain. Lake Michigan is 307 miles long and 118 miles across at its widest point. Casting into warmwater plumes in early spring when the lake temperature is still in the high 30s or low 40s has had some success. (.pdf),