This data set includes the sample site locations, site descriptions, and abiotic data used in the analyses reported in McKenna et al. 2008. The data represent selected abiotic conditions within the St. Lawrence and lower reaches of four US tributaries during 2004. Samples were collected from shallow, seinable areas (< 1.5 m) of the St. Lawrence River, adjacent wetland channels, and the lower reaches of major tributaries (Grass River, Raquette River, St. Regis River, and Salmon River). This part of the St. Lawrence River is non-tidal fresh water. Sample locations were randomly selected from a grid of spatial cells (1 km x 1 km) encompassing the area within the 5,700 ha Akwesasne Wetland Complex (at the intersection of the New York, Ontario, and Quebec borders). Continuously recording temperature (Hobo H8 one channel) and pressure (Hobo-Atm; water-level) sensors (Onset, Bourne, Massachusetts) were installed at 12 of the sites. The variability of water level was represented by the spatially interpolated coefficient of variation (CV) of those continuous water pressure measurements.