Green Lake — also known as Big Green Lake (to distinguish it from Little Green Lake, which is near Markesan) — is a lake in Green Lake County, Wisconsin, United States. Green Lake has a maximum depth of , making it the deepest natural inland lake in Wisconsin and the second largest by volume. The lake covers and has an average depth of . Green Lake has of diverse shoreline, ranging from sandstone bluffs to marshes.
History
Early settlers The Ho-Chunk Nation of Wisconsin, also sometimes referred to by the exonym, Winnebago, were some of the earliest known residents in the Green Lake Area. Green Lake, also known as Daycholah, is a spiritual place for the Winnebago. One legend describes how one must bring gifts for the Water Spirit that lives under the lake in order to enter. To clear land for the increasing number of European settlers, the Ho-Chunk people were forced to relocate by the United States government multiple times: They were moved from the Green Lake area, first to Iowa, then to Blue Earth County, Minnesota upon the establishment of a reservation for them there.
Chief Highknocker
Chief Highknocker was the last reigning chief of the Green Lake area. He was born in 1820 with the given name Henaga. He spent most of his life around the lake but was forced to move further north because of the ever-increasing number of settlers. He continued visiting Green Lake every summer with other members of the tribe. On August 12, 1911, at the age of 91, he drowned after getting a cramp while swimming in the lake. His grave at Dartford Cemetery is marked by a large boulder with an inscription from the community.
European settlement French settlers initially called the lake Lac Verde. In 1836, Wisconsin land could be purchased through the Green Bay Land Office at $1.25 per acre. Anson Dart built a dam with Smith Fowler and his own son in an effort to raise the lake level, leading to the namesake of Dartford (now called Green Lake). The next year, Dart built a sawmill that used the mill race created by the dam. The dam's success in raising lake level allowed different types of mills to be constructed around Green Lake. Many large, wooden hotels and one short-lived casino populated the north shore during the late 19th century in Green Lake, Wisconsin. One hotel was the Pleasant Point, which opened in the early 1880s. The name "Green Lake" comes from the green color of its deep waters."Wisconsin's Largest Water Areas" in Wisconsin Legislative Reference Bureau. State of Wisconsin 2005-2006 Blue Book. Madison: Wisconsin Legislature Joint Committee on Legislative Organization, 2005, p. 691. The city of Green Lake is located on the northeast shore in Dartford Bay.
Lone Tree Farm Because of the proximity to the lake, the land was ideal for farming. In 1888, Victor and Jessie Lawson purchased a plot of land called Lone Tree Point that would later become Lone Tree Farm. Victor Lawson was a newspaper editor and philanthropist, and his wife Jessie was the primary planner for their estate. Together, the Lawson's developed approximately 1,100 acres of land that is still used today as a religious conference center. Some features of the estate include roads, a boathouse, and, at the time, the largest dairy barn in Wisconsin.
Geography
The City of Green Lake, with a population of 828 as of 2018, is located on the northeast shore at the outflow of the Puchyan River. There are seven public lands and parks on or near the lake: Sunset Park, Daycholah Lookout, Dodge County Park, Hattie Sherwood Park, Deacon Mills Park, Friday Club Park, and Playground Park. The lake has three beaches: Hattie Sherwood Beach, Dodge Country Park Beach, and Sunset County Park. There are eight public access boat landings on Green Lake.
Green Lake lies within the Big Green Lake drainage basin which covers three counties. The majority of the drainage basin is in Green Lake County, with small portions of the drainage basin within the western edges of both Winnebago and Fond Du Lac counties. It lies within the Upper Fox River drainage basin, which is part of the Great Lakes drainage basin.
Spring Lake and Twin Lakes are three small lakes south of the southern shore that flow into Green Lake.
Green Lake has several bays, coves, points and peninsulas. On the northern shore, from West to East, are: Beyers Cover at the western edge of the northern shore; Sugar Loaf, a peninsula with a tall bluff; Norwegian Bay, bounded on the West by Sugar Loaf; Pigeon Cove and Malcolm Bay on the central north shore; and Dartford Bay, surrounded by the City of Green Lake at the primary outflow of the Puchyan River . Along the southern shore, from West to East: Blackbird point, a small protrusion; Dickinson Bay, a small bay on the west-central southern shore; Sandstone Bay; and Sandstone Bluff, a point that bounds Sandstone Bay on the East.
Land use in Green Lake watershed: Land CoverAcres% Total AreaAgriculture44,639.7665Open Land/Water10,665.4715.53Forest6,016.078.76Wetland3,935.175.73Suburban2,211.383.22Urban597.490.87Grassland556.280.81Barren Land48.070.07Total68,676.55100
Geology
The Green Lake basin exists within a river-carved valley that originated prior to the Wisconsin glaciation. It is likely that the movement of the glacier also deepened the valley, as well as smoothed its sides. The valley finally flooded when a recessional moraine about high blocked the exit of water at the west end of the basin during the Cary stage of glacial reduction. The basin is composed mainly of Potsdam sandstone. Beginning just below the water surface is a layer of Madison Sandstone ( thick), followed by dolomite, St. Peter Sandstone ( thick), and Trenton limestone. The shoreline is diverse, ranging from sandy beaches to swamps to steep cliffs where the bedrock is exposed, such as in the image on the left.
The glacial activity that created the Green Lake moraine also sculpted the surrounding topography. The land is covered in drumlins, parallel troughs and ridges with rolling tops that rise to a height of . These ridges are covered in a thin layer of glacial till that is composed mainly of sand eroded from the native sandstones in the area.
The water level increase caused by the dam at the head of the Puchyan has had profound impacts on the shoreline of the lake, mainly in the creation of many immature beaches. The maturity of these beaches is dictated by the composition of the shore, where looser till material erodes much more quickly than even the fragile sections of exposed bedrock. These looser areas mature more quickly. In more mature areas, boulders from the strata that are kept pushed against the shore by ice provide protection from erosion.
Hydrology Drainage basin At deep and with a volume of , Green Lake is the deepest natural inland lake in the state and second-largest by volume. Only Lake Wazee, a man-made lake, is deeper, and only Lake Winnebago has a larger volume. The deepest and steepest part of the basin is near the west end, while the eastern third is more shallow. The maximum gradient is 33% at Lucas Bluff, a large rock face on the southeast shore. There are shoals at Malcom Bay and the east end of the lake The lake has a maximum fetch of . This allows a theoretical maximum surface wave height of .
Green Lake is within the Big Green Lake Watershed, which has a catchment area is . The drainage basin lies mostly in Green Lake County, but extends east into Fond du Lac and Winnebago County. In addition to Green Lake, the drainage basin includes Spring Lake and the East and West Twin Lakes.
Tributaries and outlet The components of the Green Lake basin water budget are, in approximate percentages: direct precipitation, 51%; surface water, 41%; ground water, 8%. Eight creeks make up the surface water supply, the largest being Silver Creek, which flows into the east end of the lake. The remaining seven are Hill Creek, White Creek, Dakin Creek, Wurches Creek, Roy Creek, Spring Creek, Assembly Creek. The primary outflow is the Puchyan River, a tributary to the upper Fox River that lies in the Lake Michigan drainage basin. This makes Green Lake a drainage lake, a lake in which surface outflow dominates. A dam in the outlet keeps the water level in the lake around higher than the natural level. Green Lake has a retention time of 21 years, relatively long for a temperate lake of its size. This has implications for lake health because with very low rates of flushing, there is a large lag for reversion of fertility changes.
Water chemistry and quality
Temperature The highest recorded average temperature in 2018 was . The median ice cover duration of the last 67 seasons is 87 days. Green Lake has lost over 25 days of ice cover since 1940, and at the current rate, will continue to lose one day of ice cover every three years. At this rate, Green Lake is estimated to have zero ice cover by 2087.
Oxygen Dissolved oxygen (DO) is key to the health of aquatic ecosystems. It is essential for the metabolism of all aerobic organisms, therefore controlling their distribution, behavior, and growth within the ecosystem. If oxygen is depleted, these organisms will die or not do well. Oxygen also reacts with many other compounds, influencing their availability and chemical forms. Due to its thermal stratification, the concentration of DO in Green Lake decreases through the thermocline and into the hypolimnion. One of the most interesting characteristics of the Green Lake DO profile is a pronounced metalimnetic oxygen minimum, documented through the literature since the 1900s at a depth of and with a thickness of ~. The dissolved oxygen drops from ~9 mg/L to ~4 mg/L before rebounding and slowly decreasing into the hypolimnion. Based on other chemical characteristics such as pH and chlorophyll fluorescence at this depth, it is likely that the metalinetic oxygen minimum results from a concentration of respiring plankton. The quality of the environment can be judged by oxygen levels. Because the DO level is <5 mg/L, the lake was classified as "impaired" by the Wisconsin DNR in 2014. The low DO in this band poses a danger for aerobic organisms and has the potential to expand.
Another threat facing the lake is hypolimnetic oxygen depletion. A paleolimnological sediment analysis conducted in the deep basins of the lake showed trends of oxygen depletion since 1950. Though the deep waters are not yet devoid of oxygen, the oxygen is being depleted faster than it was in 1950. This is a result of increased nutrient (nitrogen and phosphorus) availability in the epilimnion, which increases biological productivity. As these organisms die, sink, and aerobically decompose, oxygen is depleted.
Nitrogen and phosphorus