Lake Mendota is a freshwater eutrophic lake that is the northernmost and largest of the four lakes in Madison, Wisconsin. The lake borders Madison on the north, east, and south, Middleton on the west, Shorewood Hills on the southwest, Maple Bluff on the northeast, and Westport on the northwest. Lake Mendota acquired its present name in 1849 following a proposal by a surveyor named Frank Hudson, who claimed to be familiar with local Native American languages; Lyman C. Draper, the first corresponding secretary of the Wisconsin Historical Society, proposed that 'Mendota' could have been a Chippewa word meaning 'large' or 'great.' Early history Lake Mendota originated after the Wisconsin glaciation, which occurred approximately 15,000 years ago. Glacial ice, which had covered the Madison lakes (Lakes Mendota, Monona, Kegonsa, and Waubesa) at a thickness of over 300 meters, began to retreat northwest about 14,000 years ago, damming a glacial lake near the City of Middleton that now serves as the source of water for Pheasant Branch, a creek that drains from the east into Lake Mendota. Water left behind by the retreating glaciers eventually filled the current lake bed of Lake Mendota. Although a large lake that stretched from the northern part of Lake Mendota down to Stoughton did exist for about 1,000 years, falling water levels caused this large lake to separate into the four current Madison lakes about 10,000 years ago, leaving numerous shallow-water marshes between those lakes. According to reports from European settlers in the early nineteenth century, Lake Mendota once had white sand beaches and clear water, with the sand being calcium carbonate, which continually entered the lake from its gypsum-rich watershed. However, after American settlers began to populate Madison, the physical characteristics of the once-mesotrophic lake began to rapidly change. This was largely due to the Tenney Locks, which were constructed in 1849 to regulate shipping through the Madison Isthmus and led to a four-foot increase in the water level in Lake Mendota, submerging the beaches. Additionally, due to the growth of the Wisconsin dairy industry in the late nineteenth century, Lake Mendota was repeatedly inundated with runoff from nearby farms that caused the lake bed to become dark black, the color of prairie soil. The resulting spikes in the concentrations of nitrogen and phosphorus turned Lake Mendota into a eutrophic lake. The degree of eutrophication was so high that in 1882, Edward Asahel Birge, a