Macroinvertebrate monitoring as part of the Long Term Resource Monitoring Program (LTRMP) has been conducted on the UMR Pool 13 since 1992. In this span, 37,699 targeted macroinvertebrate organisms (mayflies, fingernail clams, midges, zebra mussels, and Corbicula spp.) have been collected. Fingernail clams ranked first in total abundance from 1992 1997 with mayflies, midges, and zebra mussels ranking second, third, and fourth, respectively. Mayflies, fingernail clams, and midges reached highest densities in silt/clay substrate. Zebra mussels reached highest densities in sand and gravel/rock substrates. Targeted macroinvertebrates also exhibited preferences for habitat types and water depths. Fingernail clam and midge densities have declined dramatically after reaching peak numbers in 1993. Mayfly densities remained relatively stable during the period of research. Zebra mussel densities increased on Pool 13, reaching an all-time high of 490.6/m2 in 1997.