Abstract:
The amount of organic and the water column determines water clarity. There has been a greater interest in water clarity due to the invasion of the exotic zebra mussel (Dreissena Dolvmorpha) in the Great Lakes. This study used Secchi disk depths collected from 1970-1972 and 1981-1994 in the Indiana waters of Lake Michigan in an attempt to determine if any water clarity trends occurred which may have been attributable to the zebra mussel. The data suggests little change in water clarity between pre-zebra mussel (1970-1972 and 1981-1989) and post-zebra mussel (1990-1994) years has occurred at the four near-shore collecting sites, but interpretations of data was difficult due to variability. In fact, average Secchi disk readings in recent years (1990-1993), while variable, seemed to indicate a decline. However, the post-zebra mussel dates in 1994 at 10m, 15m, and 18m depths had the highest Secchi disk depth of visibility recorded for the study areas which may indicate the beginning of a new trend of improved depth of visibility. Additional research will be needed to determine if the 1994 improvement continues.