Isolated wetlands occur in many hydrogeomorphic settings, and while they appear to be physically isolated from other water bodies, they are almost never completely decoupled from surface-water or ground-water systems. In this paper, we examine water-quality data for isolated wetlands in three hydrogeomorphic classes (depressions, slopes, flats). Some isolated wetlands are dominated by atmospheric exchanges and have little ground-water or surface-water connections with adjacent systems. Other isolated wetlands are dominated by ground-water inputs and have intermittent or continuous hydrologic connections to adjacent systems. Water-quality characteristics of isolated wetlands are highly variable and depend primarily on the sources of water, substrate characteristics, and land uses associated with the wetland watershed. We were unable to identify any general pattern of water-quality characteristics within or between isolated wetlands in the three hydrogeomorphic classes. Alteration of hydrologic conditions (e.g., ditching, filling), however, usually results in increased nutrient export to downstream systems. From a water-quality perspective, we conclude that so-called isolated wetlands are rarely isolated, and isolation is a term that is not very useful from an ecosystem perspective. Isolated wetlands are nutrient sinks and, because most are hydrologically connected to other waters and wetlands, the loss of isolated wetlands would potentially have negative impacts on the water quality of downstream systems.