Patterns of aquatic insect activity at the surface of Waterloo Creek near Dorchester, Iowa were sampled every 4 hrs over 24 hr periods in June, July and August of 2004. Clearing nets removed all insects floating down from upstream. Four collecting nets 10 m downstream from the clearing nets captured all aquatic insects near or emerging from the water’s surface between the clearing and collecting nets. Aquatic and terrestrial insects were separated and identified to order, family and morpho-species, and quantified. Species richness, abundance, and biomass were quantified. Species richness of aquatic insects was greatest from 1200 (noon) to 1600 hrs and decreased through the night, dropping significantly in the morning from 0400 to 0800 hrs. Overall, aquatic insect abundance was greatest during morning hours from 2400 (midnight) to 1200 hrs and was lowest from 1200 to 2000 hrs. Aquatic insect biomass followed the same trend as insect abundance; it was greatest from 2400 to 1200 hrs and lowest from 1200 until 2000 hrs. These trends are the opposite of terrestrial insect results and seem to indicate a temporal resource partitioning of the surface area of the stream between aquatic insects during the morning and terrestrial insects during the evening.