The University of Michigan Biological Station has been studying 40 inland lakes in Cheboygan and Emmet Counties, Michigan, since 1972. This research effort has been designed to provide ecological and sociological information pertinent to management of these lakes and their watersheds for the enhancement of long-term environmental quality. Preliminary results of these investigations are available in Gannon and Paddock (1974). Specific information on geology, hydrology and groundwater quality was presented in Richardson (1978). Sociological data on evaluations, behaviors, and expectations of residents of the study area were reported by Marans and Wellman (1977). Instances of utilization of information generated in this project for water quality and wastewater management purposes has been documented by Pelz (1977) and Pelz and Gannon (1978). Furthermore, information written especially for lake-oriented visitors and residents has been prepared in the Biological Station’s Lakeland Report Series, Lake Profile Series, and other publications (Say et al., 1975; Foster, 1976; O’Neil, 1977). Crooked and Pickerel Lakes have been investigated since the beginning of this problem-oriented research effort. The objective of this report is to provide a summary of salient limnological features of these two water bodies. Special emphasis will be given to the current water quality and trophic status of Crooked and Pickerel Lakes and to an estimate of nutrient (phosphorus and nitrogen) sources to these lakes. Complimentary information on suitability of lakeshore soils for on-site wastewater disposal is included as Part II of this report (Gold and Gannon, 1979).