Mayflies and fingernail clams at selected sites in the UMRS Sauer, J. 1999. Mayflies (Ephemeroptera) and fingernail clams (Sphaeriidae) at selected sites in the Upper Mississippi River System. U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, February 1999. LTRMP 99-P001. 19 pp. + Appendix (NTIS #PB99-134314) ABSTRACT As part of the Long Term Resource Monitoring Program (LTRMP) macroinvertebrate component, historical sites (sites where benthic samples were previously collected by other researchers) were sampled in 1992 through 1998. Historical data on densities of the taxa were obtained from published literature and compared to data collected by the LTRMP. Temporal trends and spatial distribution in the abundance of mayflies (Ephemeroptera) and fingernail clams (Sphaeriidae) were examined in Navigation Pools 4, 8, 13, 26, and the Open River reach of the Mississippi River and La Grange Pool of the Illinois River. KEYWORDS Fingernail clams (Sphaeriidae), Long Term Resource Monitoring Program, mayflies (Ephemeroptera), spatial distribution, temporal trends