Water Quality of Lakes in Voyageurs National Park, Northern Minnesota, 1999

Water-quality samples were collected during July 1999 from selected lakes and bays, and the mouths of two rivers that flow into Voyageurs National Park in northern Minnesota. Results of laboratory analyses and field measurements of chemical and physical properties were compared to similar data collected during 1977–83. Water-quality data were evaluated for changes in specific conductance, alkalinity, nutrients, trace metals, bacteria, and trophic state. Specific conductance and alkalinity were similar to the 1977–83 period in much of the Park, but in some lakes and bays these properties may have been influenced by above normal runoff during summer 1999. Fecal-coliform bacteria colony counts were within guidelines for water-contact recreation. Nitrite plus nitrate nitrogen concentrations generally were lower throughout the Park and total phosphorus concentrations were lower in Kabetogama Lake and Black Bay relative to 1977–83. Concentrations of most trace metals were lower compared to 1977–83. Trophic state indices, based on chlorophyll a concentrations, indicated lower algal productivity throughout the Park. The largest changes in algal productivity, relative to 1977–83, were in Kabetogama Lake, Black Bay, and Sullivan Bay.