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2002 State of the Lakes Monitoring Report
The Blue Water Association (BWA) is a non-profit organization, established in 2002 to focus on monitoring and improving the water quality in Lakes Hiawatha and Nokomis in Minneapolis. Its actions are guided by recommendations of the Blue Water Commission’s Report and Recommendations, which was published in May 1998. The Blue Water Association to will issue an annual monitoring report that will that records and analyzes related water quality monitoring activities. The BWA will use the report in order to develop a baseline for future action, provide a context in which the Blue Water Association can make priorities, and evaluate progress in order to advocate for change when needed. This is the first such report.
General Characteristics of the Lakes Lake Hiawatha is a shallow temperate lake. Minnehaha Creek flows into and out of the southern end of the lake. Lake Nokomis is also a fairly shallow temperate lake. Its position in the landscape makes it susceptible to mixing from wind action. Temperate lakes have three layers throughout the summer due to temperature differences depending upon depth – this often affects dissolved oxygen and phosphorus readings at the various layers. Lakes Hiawatha and Nokomis were historically swampy marshes. Dredging of the lakes to create recreational opportunities occurred in the early 1900s. Overview Data*
Beach Bacteria Levels Fecal coliform bacteria are measured to indicate the presence of water contaminated by human or animal fecal waste. The City of Minneapolis Environmental Health Division of Regulatory Services collects water samples once or twice a week from public beaches in Minneapolis during the summer.
Elevated fecal coliform levels generally occur in lakes after rain events when the coliform from animal waste is washed into the storm sewer system that empties into the city’s lakes and creeks. These elevated levels in lakes generally return to normal levels within 48 hours of a rain event. The Minneapolis Park and Recreation Board (MPRB) recommends that people refrain from swimming at beaches for 48 hours after a rain event. Fecal coliform at beaches can also occur directly from incorrect diaper handling procedures, geese and other waterfowl, and from raccoon, squirrel, cat and dog waste. MPRB has signs posted at beaches to remind people to use swim diapers, keep their dogs out of the beaches, and pick up their pet waste. The state of Minnesota water quality guidelines for fecal coliform in waters used for recreational body contact are: “not to exceed 200 organisms per 100 mL as a geometric mean of not less than 5 samples in any calendar month, nor shall more than 10% of all samples for any calendar month individually exceed 2,000 organisms per 100 mL.” This standard only applies between May 1 and October 31.” These guidelines have not been adopted by the City of Minneapolis.. Fecal coliform results are presented in Table 1. The shaded cells in Table 1 contain values that exceed 2,000 organisms per 100 mL. It was not appropriate to calculate geometric means for Minneapolis public beaches because of the sampling schedule. Table 1. Fecal coliform results for 2002 (units are number of bacteria per 100 mL sample).
The beach at Lake Hiawatha exceeded the state public health guidelines five times in 2002 (shaded areas). The high number on July 8th could be a result of it being the Monday after the 4th of July weekend (with temperatures in the high-80’s to mid-90’s) with heavily used beaches the four days before these samples were taken. The main beach at Lake Nokomis had one exceedance and the East beach had no exceedances. No beaches in Minneapolis were closed in 2002. No reports of illness due to swimming at the beaches were received. With continued monitoring and education programs, the public beaches will continue to be a valuable resource to Minneapolis residents.
Lake Water Clarity Water transparency or clarity is measured with a black and white disc called a Secchi disc. The Secchi disc is lowered into the water until it cannot be seen; the depth at which it is no longer visible is called the Secchi transparency. Secchi transparency is measured weekly by MPRB staff during the growing season of May through September. Results for 2002 are given in Table 2. Table 2. Average monthly Secchi transparency in feet for 2002.
Similar to most lakes that are surrounded by urban development, Lakes Hiawatha and Nokomis are eutrophic, meaning they are rich in nutrients. Storm sewer discharge is the major contributor of nutrients and other contaminants into the two lakes. As storm water flows across lawns and down streets, it captures excess fertilizer, soil particles, pet waste, leaves, grass clippings, oil and a magnitude of other nutrients and contaminants. Until 2000, storm water was discharged into Lakes Nokomis and Hiawatha without any treatment. In 2000 and 2001, to help clean up water before entering the lakes, the Minnehaha Creek Watershed District (MCWD) installed three wetland ponds and two grit chambers near Lake Nokomis and the MPRB installed a pond water hazard in the golf course on the west side of Lake Hiawatha. Lake Hiawatha had fairly stable clarity for the year, averaginging four feet. Nokomis had fairly clear water in June and July but declined in August and September. Algae blooms in these lakes most often affect clarity. People generally perceive clarity of around four feet as the minimum acceptable for swimming. A reasonable goal for Lakes Hiawatha and Nokomis is a Secchi transparency of 4 to 7 feet.
Trophic State Index (TSI) Lake fertility or trophic state is estimated by using water quality measurements and mathematical formula called a Trophic State Index (TSI), developed by Dr. Bob Carlson (1977, University of Minnesota). TSI formulas are calculated from three different lake measurements: water transparency, chlorophyll-a levels and phosphorus levels.
Water transparency is as straightforward as it sounds – it is a measurement of the depth that a person can see into a lake. A black and white disk, called a Secchi disk is lowered into the lake on a string or chain marked with inches. The lower the Secchi disk is visible, the clearer the water. Chlorophyll-a is the green pigment in plants that is essential for photosynthesis. A measure of its presence in water estimates algae abundance. Phosphorous is a compound found commonly in nature and is essential for the growth of plants and other living matter. Increased phosphorus is related closely to increased algae, frequency of algal blooms and increased quantity of blue-green algae. There are five common sources of phosphorus in Lake Nokomis and Lake Hiawatha: soils, plants (e.g. leaf litter and lawn clippings), lawn fertilizer, animal waste, and existing lake loads. When these measurements are used in the TSI formula, they produce a score from 0 to 100. Higher numbers indicate a more fertile lake. Lakes with TSI scores below 25 often look like sandy swimming pools while lakes with TSI scores above 75 will be more like pea soup, having a very dense aquatic plant growth. In the Twin Cities metro area, it is recommended that a TSI score of 59 or lower be maintained at lakes used for swimming. According to the MPRB, over the last 10 years (1991-2001), using TSI scoring, Lake Nokomis and Lake Hiawatha showed no significant changes in water quality. Figure 1. Historical High TSI scores for Lakes Hiawatha, Isles and Nokomis over the last 10 years. Source: MPRB.
Lake Levels and Dam Fluctuations In 2001, the MCWD installed an inflatable weir where Lake Nokomis drains into Minnehaha Creek. When water levels reach 814.7 feet above sea level in Minnehaha Creek the weir is automatically inflated, thereby preventing polluted water from Minnehaha Creek from flowing into Lake Nokomis. As the creek level decreases, the weir deflates and water is allowed to flow from Lake Nokomis into the creek. Lake Hiawatha levels are largely controlled by creek flow.
Surrounding Area Activities Affecting the Lakes Water quality improvement in Lakes Hiawatha and Lake Nokomis requires a long-term and committed partnership between residents and the organizations active in resource management. While much has been done, activities such as the following need to continue to see on achieve long-term improvements in water quality. The following projects and activities are currently being implemented by the City of Minneapolis, the MPRB, and the Minnehaha Creek Watershed District will have a positive impact on water quality in Lakes Nokomis and Hiawatha:
Fisheries Update
It is expected that the Minnesota Department of Natural Resources will conduct a fisheries survey of Minnehaha Creek in 2003. The most recent DNR fisheries survey for Lake Hiawatha and Lake Nokomis was in 1995. There is a fish advisory for children under 15, pregnant women and women who may become pregnant. Fish, especially bottom feeders, can bio-accumulate lead, mercury and other heavy metals and PCBs. It is not recommended that individuals eat more than one serving of fish per month from these lakes. Lake Nokomis is not able to support reproduction of walleyes because of the windswept, shallow shoreline – annual stocking is the only option at this time. Lake Hiawatha is naturally stocked when fish enter through Minnehaha Creek and are often flushed from the lake into the Mississippi River in rainy periods. Generally, it can be expected that as phosphorous is lowered and the shorelines are improved that the fisheries will improve.
Minnehaha Creek Report Minnehaha Creek has five sites that are monitored for macro invertebrates (water insects and assorted pupa) as part of a volunteer stream-monitoring program. The results indicate fair to good water quality (2001 Hennepin County River Watch Results). The MPRB cooperates with the Metropolitan Council and the MCWD in the operation of a Watershed Outlet Monitoring Program (WOMP) station on Minnehaha Creek, located at 32nd Ave S and Minnehaha Parkway, downstream of Lake Hiawatha. The flow data and water quality data collected at this station are used as part of a Metropolitan Council program that establishes pollutant loading goals for streams that drain into the Mississippi River, part of an Environmental Protection Agency National Pollutant Discharge Elimination System (NPDES) permit.
(c)
2003, Nokomis East Neighborhood Association, Inc.,
and Blue Water Association, Inc.
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