Water-quality data at two unnamed lakes at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota, 2019

The National Crude Oil Spill Fate and Natural Attenuation Research Site is located near where about 1.7 million liters of crude oil spilled in 1979. Much of the oil spill leached into groundwater which flows towards an unnamed lake at the site. The U.S. Geological Survey Branch of Hydrogeophysics has been working to map the plume's extent on land and into the lake using a variety of geophysical techniques. In 2018, the group was able to map a group of anomalies within the lake consisting of elevated specific conductance concentrations. It was determined that these specific conductance anomalies were likely attributed to hydrocarbon plumes leaching into the lake. In 2019, the U.S. Geological Survey Central Midwest Water Science Center deployed an Ecomapper Autonomous Underwater Vehicle (AUV) and two EXO2 multi-parameter sondes to directly measure basic water quality parameters using several different approaches. These data were used for comparison to indirect geophysical measurements and to characterize water quality within the main unnamed lake (north lake) and a nearby smaller unnamed lake (south lake).