Comprehensive Long Lake Creek Feasibility Study

Long Lake Creek is a resource of the Minnehaha Creek Watershed, located within the Twin Cities' communities of Long Lake and Orono. This perennial stream originates as the outlet of Long Lake, flowing and terminating at the confluence with Tanager Lake. Tanager Lake is connected to Brown's Bay and the famed Lake Minnetonka system (Figure 1). The headwaters of Long Lake. From there it flows approximately 2.7 miles south through wetland and forested areas of Orono to its mouth at Tanager Lake, which discharges to Browns Bay on Lake Minnetonka. Long Lake Creek drains approximately 8,200 acres. The lower 1 mile of Long Lake Creek is part of County Ditch 27 (see County Ditch 27 in Figure 2), established in 1915 for agricultural drainage purposes and transferred to MCWD in 1972. Long Lake Creek is included in the District's Annual Hydrologic Data monitoring program, and was studied in-depth in 2004 as part of the District's Upper Watershed Stream Assessment.. The Stream Assessment identified six storm sewer outfalls, sixteen sites of localized erosion, and the fourteen sites with debris in the channel. Many of the erosion sites were concentrated in Reaches 2 and 5 and were investigated as part of EOR's previous feasibility study (see Appendix A). Water quality in the creek is monitored at two locations (see Figure 2). Phosphorus load is generally greater at the downstream site., suggesting that the watershed or in-line wetlands are contributing to phosphorus loads in the creek and thus to Tanager Lake. Tanager Lake serves mainly as a pretreatment basin for discharges to Brown's Bay. Dissolved oxygen within the stream in the summer months tends to fall down below the mg/L State of Minnesota standard for class 2B waters. The 2007 MCWD Comprehensive Plan identifies an interim in-lake total phosphorus concentration goal of 70 ug/L for downstream Tanager Lake. The state standard, and thus the long-term goal for Long and Tanager Lake, is 40 ug/L. The mean summer 2009 total phosphorus concentration was 85.2 ug/L, well in excess of the District's 70 ug/L interim goal. It is likely that phosphorus from Long Lake Creek is contributing to the high in-lake concentration in Tanager. Tanager Lake was placed on the State Impaired Waters List in 2010 because of its poor water quality. According to the 2007 MCWD Comprehensive Plan, loading to Tanager Lake will need to be reduced by 923 pounds of phosphorus per year in order to meet the interim phosphorus concentration goal.