Diatoms comprise the major group of algae in Iowa waters. Their ecological significance, important in pollution evaluation studies, cannot be fully appreciated without a thorough knowledge of their taxonomy. A scale for abundance rating was used giving at least a rough estimate if data permitted. The names of 50 diatom genera occurring in Iowa are listed and for each genus, the number of taxa in the master list and the number in the 'more common' list are presented. A pollen analysis is tabulated; the samples in this analysis extended through 35 ft. of sediment to the postglacial interface at Little Miller's Bay, Lake West Okoboji. Dating was conducted by the radiocarbon technique for samples taken between 34 ft. and 35 ft. in the sediment core. Since this level had the maximum spruce pollen concentration and the pollen percentage decreased progressively above this level, it was considered as the postglacial interface. Some interesting problems lie in consideration of those diatoms which have disappeared from the original lake flora and those which have become common only since the middle of the postglacial period.