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Of all the thousands of lakes in Minnesota, the DNR and University of Minnesota scientists have identified just 176 that they think will be cold and deep enough for cisco to survive in when temperatures continue to rise. These 'refuge lakes' are planned to be the last sanctuary and stand for the cisco, a small type of whitefish that's popular to catch during ice fishing and is a key food source for healthy walleye, muskie and pike populations. The DNR does regular sampling and testing of water temperature and oxygen levels as well as counts of cisco in these refugee lakes to keep an eye on population numbers. On July 18, 2019 biologists from Sentinel Lakes placed nets in Elk Lake in Itasca State Park to catch and count cisco. That night acoustic sonar testing was performed and the nets were pulled up and fish counted the following morning.