Observations of shoaling and feeding behavior of the zooplanktivorous June sucker, Chasmistes liorus, were made during summer 2003 in Red Butte Reservoir, Utah. Water clarity limited observations to 0.5–1.5 m below the water surface. Schools of adult suckers, ranging from a few to >200 fish, were observed on 20 days from May to September. I classified them as schools rather than shoals because the groups moved synchronously rather than appearing simply as an aggregation of fish. These schools were near the water surface, generally in areas of the reservoir with a water depth of >3 m, and presumably fed on the zooplankton in the epilimnion. Juvenile suckers (age-1 and age-2) were observed only on a few occasions, near inundated vegetation. Age-0 suckers were observed in large shoals (aggregations of hundreds of fish) near the surface in the shadows of inundated vegetation in July and August. Juvenile suckers (age-0, age-1, and age-2) were always observed in age-specific shoals, while suckers in adult schools had a wider range of sizes.