Lake Assessment Program - Green Lake, Isanti County

Green Lake is located 10.5 miles west of Cambridge in Isanti County. The lake is basically oval shaped and has a surface area of about 800.8 acres. Land use in the watershed is primarily characterized by wetlands (-53 percent) and agriculture (-27 percent). The watershed is relatively small (19 sq. miles) compared to the surface area of the lake (15.2:1 ratio). The land use composition is fairly typical for the lakes in this region of the state - North Central Hardwood Forests ecoregion. A number of wetlands and a significant forest percentage (-9 percent) exists in the watershed which can serve to trap nutrients and sediments arising from the watershed. Green Lake was sampled during the summer of 1991 by Minnesota Pollution Control Agency (MPCA) staff and citizens from the Green Lake Improvement Association (Association). Water quality data collected during the study indicates the lake is eutrophic with a mean total phosphorus concentration of 43 ?g/L, mean chlorophyll! of 25.3 ?g/L and new Secchi transparency of 4.9 feet. The total phosphorus value is on the upper range of values found in representative minimally impacted lakes in the North Central Hardwood Forests ecoregion. The chlorophyll! concentration is slightly higher than expected based on the phosphorus concentration. This may be related to the higher than normal precipitation for 1991. Higher precipitation means more runoff and higher phosphorus loading which can contribute to increased algae growth and lower Secchi transparency.