Studies of the Common Loon (Gavia immer) during its breeding season on northern freshwater lakes in North America have suggested that water quality has an influence on breeding and foraging success. Less is known, however, about the effects of water quality on loon behavior during the winter, which is spent in estuarine and marine environments. In this study, we investigated the effects of water clarity and tidal stage on loon diving behavior at seven sites along a Maryland estuary. At each site, the total number of loons observed and mean dive durations of individuals were measured and compared to various measurements of water clarity, including Secchi depth and turbidity, and to tidal stage. Dive durations were positively associated with Secchi depth, which indicates that birds dove for longer periods in areas with higher water clarity. Dives were also longer during low tide in comparison to other tidal stages. No relationship was found between aspects of water clarity and the distribution of wintering loons.