Sentinel Lake Assessment Report South Twin Lake (44-0014) Mahnomen County, Minnesota

The Minnesota Pollution Control Agency (MPCA) is working in partnership with the Minnesota Department of Natural Resources (MDNR) on the Sustaining Lakes in a Changing Environment (SLICE) Sentinel Lakes Program. The focus of this interdisciplinary effort is to improve understanding of how major drivers of change such as development, agriculture, climate change, and invasive species can affect lake habitats and fish populations, and to develop a long-term strategy to collect the necessary information to detect undesirable changes in Minnesota lakes (Valley 2009). To increase our ability to predict the consequences of land cover and climate change on lake habitats, SLICE utilizes intensive lake monitoring strategies on a wide range of representative Minnesota lakes. This includes analyzing relevant land cover and land use, identifying climate stressors, and monitoring the effects on the lake's habitat and biological communities. The Sentinel Lakes Program has selected 24 lakes for long-term intensive lake monitoring (Figure 1). The "Deep" lakes typically stratify during the summer months only. "Shallow" lakes are defined as mixing continuously throughout the summer. "Cold Water" lakes are defined as lakes that both harbor cisco, lake whitefish, or lake trout and are the focus of research funded by the Environment and Natural Resources Trust Fund (ENTF). "Super Sentinel" lakes also harbor cold-water fish populations and research on these lakes is also funded by the ENTF. South Twin Lake was selected to represent a coldwater, mesotrophic lake in the Northern Lakes and Forests (NLF) ecoregion. South Twin Lake is a 452 hectare (1,118 acre lake) and is located south of Naytah- waush in Mahnomen County. It lies within the Wild Rice River major watershed. South Twin Lake has a maximum depth of 8.8 meters (29 feet) and a mean depth of 3.7 meters (12 feet). The lake is 47% littoral with one public access on the western shore. The total contributing watershed for South Twin Lake is 2,724 hectares (6,743 acres).