Eagle Lake 29-0256-00 HUBBARD COUNTY
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Eagle Lake 29-0256-00 HUBBARD COUNTY Lake Water Quality Summary Eagle Lake is located about nine miles north of Park Rapids, Minnesota. It covers 411 acres and has a long, narrow shape. Eagle Lake has one inlet and one outlet, which classifies it as a drainage lake. The inlet enters on the north side of the lake from Island Lake. The outlet flows out of the south end into Potato Lake. From Potato Lake, the Potato River joins the Fish Hook River, which eventually joins the Shell River and then the Crow Wing River. Water quality data have been collected on Eagle Lake since 1991 (Table 3). These data show that the lake is mesotrophic, which is characterized by moderately clear water throughout the summer and excellent recreational opportunities. The Eagle Lake Association is involved in many activities, including water quality monitoring. They are also a member of the Hubbard Coalition of Lake Associations (COLA). Table 1. Eagle Lake location and key physical characteristics. Location Data Physical Characteristics MN Lake ID: 29-0256-00 Surface area (acres): 411 County: Hubbard Littoral area (acres): 164 Ecoregion: Northern Lakes & Forests % Littoral area: 40% Major Drainage Basin: Upper Mississippi River Max depth (ft), (m): 77, 23.5 Latitude/Longitude: 47.03000000 / -95.09972222 Inlets: 1 Invasive Species: None Outlets: 1 Public Accesses: 1 Table 2: Availability of data and an observation of the quantity of sample points. Data Availability Excellent data set through the Citizens Lake Transparency data Monitoring Program. Excellent data set through the RMB Lab Lakes Chemical data Program. Inlet/Outlet data No inlet or outlet data exist for this lake. Recommendations For recommendations refer to page 18. RMB Environmental Laboratories, Inc. 1 of 19 2012 Eagle Lake Lake Map Figure 1. Map of Eagle Lake with 2010 aerial imagery and illustrations of sample site locations, inlets and outlets, and public access points. The light green areas in the lake illustrate the littoral zone, where the sunlight can usually reach the lake bottom allowing aquatic plants to grow. Table 3. Monitoring programs and associated monitoring sites. Monitoring programs include the Citizens Lake Monitoring Program (CLMP) and RMB Environmental Laboratories Lakes Program (RMBEL). Lake Site Depth (ft) Monitoring Programs 201 50 CLMP: 1991-2010 202 77 CLMP: 1993, 1997-2011; RMBEL: 1997-2011 RMB Environmental Laboratories, Inc. 2 of 19 2012 Eagle Lake Water Quality Characteristics - Historical Means and Ranges Table 4. Water quality means and ranges for primary sites. Primary Parameters Site Site 201 202 Total Phosphorus Mean (ug/L): 19 Total Phosphorus Min: 5 Total Phosphorus Max: 37 Number of Observations: 72 Chlorophyll a Mean (ug/L): 7 Chlorophyll-a Min: 1 Chlorophyll-a Max: 18 Number of Observations: 71 Secchi Depth Mean (ft): 10.3 9.8 Secchi Depth Min: 6.0 6.5 Secchi Depth Max: 27.0 17.5 Number of Observations: 203 175 Figure 2. Eagle Lake total phosphorus, chlorophyll a and transparency historical ranges. The arrow represents the range and the black dot represents the historical mean (Primary Site 202). Figure adapted after Moore and Thornton, [Ed.]. 1988. Lake and Reservoir Restoration Guidance Manual. (Doc. No. EPA 440/5-88-002) RMB Environmental Laboratories, Inc. 3 of 19 2012 Eagle Lake Transparency (Secchi Depth) Transparency is how easily light can pass through a substance. In lakes it is how deep sunlight penetrates through the water. Plants and algae need sunlight to grow, so they are only able to grow in areas of lakes where the sun penetrates. Water transparency depends on the amount of particles in the water. An increase in particulates results in a decrease in transparency. The transparency varies year to year due to changes in weather, precipitation, lake use, flooding, temperature, lake levels, etc. The annual mean transparency for Eagle Lake ranges from 7.6 – 13.9 ft (Figure 3). Transparency is almost identical every year at sites 201 and 202 except for in 2000. This shows that water quality conditions are very similar between the north and south ends of the lake. Transparency monitoring should be continued at both sites to track water quality in Eagle Lake. Transparency: Annual Means 16 14 12 (ft) 10 8 Depth 6 Site 201 Secchi 4 Site 202 2 Long‐term Mean, site 202 0 Figure 3. Annual mean transparency for sites 201 and 202. Eagle Lake transparency ranges from 10 to 27 feet throughout the summer. Figure 4 shows the seasonal transparency dynamics. The transparency does not change much throughout the summer for Eagle Lake. The maximum Secchi reading is usually obtained in early summer. Eagle Lake transparency is high in May and June and declines slightly through August. The transparency then rebounds in October after fall turnover. The dynamics have to do with algae and zooplankton population dynamics, and lake turnover. It is important for lake residents to understand the seasonal transparency dynamics in their lake so they are not worried about why their transparency is lower in August than it is in June. It is typical for a lake to vary in transparency throughout the summer RMB Environmental Laboratories, Inc. 4 of 19 2012 Eagle Lake Seasonal Transparency Dynamics 1993 30 1997 28 1998 26 1999 24 22 2000 20 2001 (ft) 18 2002 16 2003 Depth 14 2004 12 2005 Secchi 10 2006 8 2007 6 2008 4 2009 2 2010 0 2011 Pattern Poly. (Pattern) Figure 4. Seasonal transparency dynamics and year-to-year comparison (site 202). The black line represents the pattern in the data. User Perceptions When volunteers collect secchi depth readings, they record their perceptions of the water based on the physical appearance and the recreational suitability. These perceptions can be compared to water quality parameters to see how the lake "user" would experience the lake at that time. Looking at transparency data, as the secchi depth decreases the perception of the lake's physical appearance rating decreases. Eagle Lake was rated as being "not quite crystal clear" 90% of the time between 1991-2011 (Figure 5). Physical Appearance Rating 5% 2% 3% 3% Crystal clear water 90% Not quite crystal clear – a little algae visible 5% Definite algae – green, yellow, or brown color apparent 2% High algae levels with limited clarity and/or mild odor apparent 0% Severely high algae levels 90% Figure 5. Physical appearance rating, as rated by the volunteer monitor. RMB Environmental Laboratories, Inc. 5 of 19 2012 Eagle Lake As the secchi depth decreases, the perception of recreational suitability of the lake decreases. Eagle Lake was rated as being "beautiful" 11% of the time from 1991-2011. Recreational Suitability Rating 5% 1% 11% 11% Beautiful, could not be better 83% Very minor aesthetic problems; excellent for swimming, boating 5% Swimming and aesthetic enjoyment of the lake slightly impaired because of algae levels 1% Desire to swim and level of enjoyment of the lake substantially reduced because of algae levels 0% Swimming and aesthetic enjoyment of the lake nearly impossible because of algae levels 83% Figure 6. Recreational suitability rating, as rated by the volunteer monitor. Total Phosphorus Eagle Lake is Total Phosphorus 1997 40 phosphorus limited, 1998 which means that algae 35 Eutrophic 1999 and aquatic plant 2000 growth is dependent 30 2001 ppb) upon available 2002 phosphorus. 25 2003 (ug/L, Total phosphorus was 2004 20 evaluated in Eagle 2005 Lake in 1997-2011. Mesotrophic 2006 15 2007 Phosphorus Most of the data points 2008 fall into the mesotrophic 10 range (Figure 7). Total 2009 2010 5 Oligotrophic There are a large range 2011 of phosphorus 0 Mean concentrations in Eagle Lake. Some years, such as 2000, are very low, while other years, Figure 7. Historical total phosphorus concentrations (ug/L) at site 202 for Eagle Lake. such as 2002, are high. Eagle Lake has a very large watershed (218 times larger than the lakeshed), and it could be that precipitation and conditions in the watershed are responsible for the phosphorus dynamics in the lake. The transparency is inversely related to the total phosphorus in Eagle Lake. For example, in 2000 when the phosphorus readings were abnormally low, the transparency readings were very high. Phosphorus should continue to be monitored to track any future changes in water quality. RMB Environmental Laboratories, Inc. 6 of 19 2012 Eagle Lake Chlorophyll a Chlorophyll a is the 25 1997 pigment that makes plants Chlorophyll a 1998 and algae green. 1999 Chlorophyll a is tested in 20 2000 ppb) 2001 lakes to determine the algae concentration or how 2002 15 2003 "green" the water is. (ug/L, a 2004 Chlorophyll a 10 2005 concentrations greater 2006 than 10 ug/L are perceived 2007 as a mild algae bloom, Chlorophyll 5 2008 while concentrations 2009 greater than 20 ug/L are 2010 0 perceived as a nuisance. 2011 Minor Algae Chlorophyll a was Nuisance Algae evaluated in Eagle Lake in Figure 8. Chlorophyll a concentrations (ug/L) for Eagle Lake. 1997-2011 (Figure 8). Chlorophyll a concentrations reached 10 ug/L most years, indicating minor algae blooms in August-September. Dissolved Oxygen Dissolved Oxygen (mg/L) Dissolved Oxygen (DO) is the amount of oxygen dissolved 0246810in lake water. Oxygen is necessary for all living organisms to survive except for some bacteria. Living organisms 0 breathe in oxygen that is dissolved in the water. Dissolved Temperature (F) 3 oxygen levels of <5 mg/L are typically avoided by game Dissolved Oxygen (mg/L) fisheries. 6 9 Eagle Lake is a moderately deep lake, with a maximum 12 depth of 77 ft. Dissolved oxygen profiles from 2007 indicate that Eagle Lake stratifies in the summer (Figure 9).