Urbanization and residential sprawl are raising concerns of the effects of land use and development on lake health and water quality. The Seattle region of the Puget Sound lowlands has experienced rapid growth, and hosts a large number of small lakes. This study conducted a land use analysis within 80 small lake watersheds in King County, Washington, U.S.A.

Water quality data (Secchi depth, Chlorophyll-a concentration, total phosphorus concentration) were obtained for these lakes. A variety of other data were also obtained, including: hydraulic retention time; whether the watershed relies upon sewer or septic systems for wastewater treatment; land uses within lakeshore and riparian buffers in the watersheds; development density along lakeshores; and average lake depth.

A large proportion of high density development within watersheds surprisingly was correlated to improved water quality, and a large proportion of low density and forested land uses were correlated to degraded water quality. In addition, watersheds that relied on sewer systems were found to have better water quality than watersheds that relied on septic systems. Longer hydraulic retention time was also correlated with improved water quality.

The results suggest several mechanisms that could be affecting water quality. Surface water management and drainage plans, which are implemented in areas of high density development, could be succeeding in protecting surface water quality. The morphology and nature of the lakes play a large role in water quality. In general, the results of this study suggest that a variety of processes affect water quality in lakes, and the complex and interwoven processes are not easily described by general relationships or simplified hypotheses.