Primary production and light availability in Lake Onalaska: Owens, J. L., and W. G. Crumpton. 1993. Primary production and light availability in Lake Onalaska: Results of a pilot study to evaluate continuous water quality monitors for use in Upper Mississippi River backwaters. Report by Iowa State University, Ames, Iowa, for the U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, November 1993. EMTC 93-S015. 74 pp. (NTIS #PB94-125994) ABSTRACT To evaluate the performance of a continuous monitoring device (Waterlogger) developed at Iowa State University, a pilot study was conducted on Lake Onalaska, Wisconsin (Navigational Pool 7 of the Upper Mississippi River), between June 28 and October 4, 1990. The devices recorded subsurface (20 cm) temperature and dissolved oxygen and surface and subsurface (50 cm) light (photon flux of photosynthetically active radiation) every 6 minutes at eight sites. The Waterlogger device stores its measurements electronically on battery-powered memory (RAM) within the unit and can transmitted the recorded data directly to a personal computer. Conversion of the Waterlogger readings to calibrated engineering units is achieved by additional processing of the data via specific conversion equations developed by the user for each device. The Waterloggers were durable and reliable generally, and suffered no electronic malfunctions. Two of units exhibited minor leakage and several oxygen probes exhibited a manufacturing defect during this test. These problems were easily corrected. Two Waterloggers kept in close proximity (5-m separation) during the study generated highly dynamic, and closely parallel oxygen data with regular diurnal patterns. Temperature data from the units generally compared well with field reference values. The performance of the units with regard to light was difficult to evaluate due to the highly variable nature of this parameter, but results seemed reasonable. The authors recommend that a network of Waterloggers be established on the Upper Mississippi River and that this network should initially include the six trend-analysis pools currently being monitored by the Long Term Resource Monitoring Program. KEYWORDS Upper Mississippi River System, LTRMP, continuous monitoring, water quality, dissolved oxygen, water temperature, underwater light