Water Quality of Rogers Lake, Dakota County, Minnesota

Construction of an interstate highway is planned near Rogers Lake in Dakota County, Minn. Samples of water and bed material were collected at six sites during March 1976 to April 1978 to determine selected physical, chemical, and biological characteristics before construction. Samples were collected at least twice during each season of the year. Data derived from these samples will provide baseline information to aid in assessing the impact of highway construction on the water quality of the lake. Rogers Lake is separated into an upper and lower lake by a culvert; both were eutrophic and dominated by blue-green algae year around. The upper lake is a closed basin; it is shallower and contains less water than the lower lake and had higher concentrations of dissolved solids, nitrogen, and phosphorus. Phytoplankton cell counts were also higher in the upper lake. Analyses of water from Rogers Lake suggest that sodium and chloride concentrations were higher than in ground water or in water in some surrounding lakes. Sodium ranged from 7.2 to 55 milligrams per liter, and chloride ranged from 15 to 130 milligrams per liter. Concentrations were highest in March 1978, when most of the lake water was frozen. Much of the sodium and chloride may have been derived from road salts used for deicing.