Cass Lake 04-0030-00 BELTRAMI COUNTY Lake Water Quality Summary Cass Lake is located at the city of Cass Lake, MN, and spans both Cass and Beltrami Counties. It covers 15,958 acres and is the 8th largest lake in Minnesota in terms of surface area. Cass Lake has four inlets and one outlet, which classify it as a drainage lake. Water enters Cass Lake from the Mississippi River, Kitchi Lake, Pike Bay, and a ground-fed stream in the northeast. The Mississippi River enters and exits Cass Lake. Cass Lake water levels are affected by the operation of two dams on the Mississippi River. Otter Tail Power Company operates a dam upstream, just below Stump Lake. At the Cass Lake outlet is Knutson Dam, owned and operated by the U.S. Forest Service. A Superfund cleanup site exists on Pike Bay near the south side of Cass Lake. Water quality data have been collected on Cass Lake at various sites from 1979-2015 (Tables 2 & 3). These data show that the lake is mesotrophic (TSI = 44) with moderately clear water conditions most of the summer and excellent recreational opportunities. Cass Lake does not have an association. Its water quality is managed by the Leech Lake Band of Ojibwe Division of Resource Management. Table 1. Cass Lake location and key physical characteristics. Location Data Physical Characteristics MN Lake ID: 04-0030-00 Surface area (acres): 15,958.26 County: Beltrami Littoral area (acres): 7,597.73 Ecoregion: Northern Lakes and Forests % Littoral area: 47.61 Major Drainage Basin: Mississippi R. - Headwaters Max depth (ft), (m): 120 ft, 36.58 m Latitude/Longitude: 47.4227/-94.54775 Inlets: 5 Invasive Species: zebra mussel, starry Outlets: 1 stonewart Public Accesses: 4 Table 2. Availability of primary data types for Cass Lake. Data Availability Transparency data Good data set from 2005-2015. Chemical data Fair data set from various years. Inlet/Outlet data Good data set, with the last data collected in 2009. Recommendations For recommendations refer to page 21. RMB Environmental Laboratories, Inc. 1 of 23 2017 Cass Lake Lake Map Figure 1. Map of Cass Lake with 2010 aerial imagery and illustrations of lake depth contour lines, 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 Lake Monitoring Program Project (LMPP), Citizen Lake Monitoring Program (CLMP), Cass Lake CWP (CWP), Itasca County Grand Rapids SWAG (SWAG), and RMB Environmental Laboratories Lakes Program (RMBEL). Lake Site Depth (ft) Monitoring Programs 101 5 RMBEL: 2004-2005, LMPP: 2007 204 110 CLMP: 1988-1993, 1997-2000 205 50 CLMP: 1993-1994, 1997-1999 208 90 CWP: 1999-2000; CLMP: 2004-2006 209 25 CLMP: 2004-2006 210 * Primary Site 35 CLMP: 2005-2015 211 45 CLMP: 2006-2011 212 85 CLMP: 2008-2011 215 *Secondary Site 115 SWAG:2013-2014 RMB Environmental Laboratories, Inc. 2 of 23 2017 Cass Lake Average Water Quality Statistics The information below describes available chemical data for Cass Lake through 2016 (Table 4). Data for secchi depth is from primary site 210 while total phosphorus and chlorophyll a, are from the secondary site 215. Minnesota is divided into 7 ecoregions based on land use, vegetation, precipitation and geology. The MPCA has developed a way to determine the "average range" of water quality expected for lakes in each ecoregion. For more information on ecoregions and expected water quality ranges, see page 11. Cass Lake is in the Northern Lakes and Forests Ecoregion. Table 4. Water quality means compared to ecoregion ranges and impaired waters standard. Impaired Ecoregion Waters Parameter Mean Range1 Standard2 Interpretation Total phosphorus (ug/L) 15.7 14 – 27 > 30 3Chlorophyll a (ug/L) 4.4 4 – 10 > 9 Results are within the expected range for the Northern Lakes Chlorophyll a max (ug/L) 8.7 < 15 and Forests Ecoregion. Secchi depth (ft) 9.0 8 – 15 < 6.5 Dissolved oxygen See page 8 Dissolved oxygen depth profiles show that the lake mixes in spring and fall (dimictic). Total Kjeldahl Nitrogen 0.5 <0.4 – 0.75 Indicates insufficient nitrogen to (mg/L) support summer nitrogen- induced algae blooms. Alkalinity (mg/L) 147.9 40 – 140 Indicates a low sensitivity to acid rain and a good buffering capacity. Color (Pt-Co Units) NA 10 – 35 No data available. pH 8.2 7.2 – 8.3 Within the expected range for the ecoregion. Lake water pH less than 6.5 can affect fish spawning and the solubility of metals in the water. Chloride (mg/L) 3.4 0.6 – 1.2 Slightly above the ecoregion range and could indicate watershed loading. Total Suspended 2 <1 – 2 Indicates low suspended solids Solids (mg/L) and clear water. Specific Conductance 318 50 – 250 Slightly above the ecoregion (umhos/cm) range and could indicate watershed loading. TN:TP Ratio 31.8:1 25:1 - 35:1 Within the expected range for the ecoregion, and shows the lake is phosphorus limited. 1The ecoregion range is the 25th-75th percentile of summer means from ecoregion reference lakes 2For further information regarding the Impaired Waters Assessment program, refer to http://www.pca.state.mn.us/water/tmdl/index.html 3Chlorophyll a measurements have been corrected for pheophytin Units: 1 mg/L (ppm) = 1,000 ug/L (ppb) RMB Environmental Laboratories, Inc. 3 of 23 2017 Cass Lake Water Quality Characteristics - Historical Means and Ranges Table 5. Water quality means and ranges for primary sites. Primary Site Secondary Site Parameters 210 215 Total Phosphorus Mean (ug/L): NA 15.7 Total Phosphorus Min: 12 Total Phosphorus Max: 22 Number of Observations: 11 Chlorophyll a Mean (ug/L): NA 4.4 Chlorophyll-a Min: 2 Chlorophyll-a Max: 8.7 Number of Observations: 11 Secchi Depth Mean (ft): 9 11 Secchi Depth Min: 5.5 7.9 Secchi Depth Max: 21 14.1 Number of Observations: 150 8 FigureFigure 2. Cass 2. Lake Lake “insert” total phosphorus,total phosphorus, chlorophyll chlorophyll a and a transparency and transparency historical historical ranges. ranges. The arrow The arrow representsrepresents the therange range and and the theblack black dot dotrepresents represents the thehistorical historical mean mean (Primary (Primary Site Site 210 xxx). and SecondaryFigure adapted after Moore and Thornton, [Ed.]. 1988. Lake and Reservoir Restoration Guidance Manual. (Doc. No. EPA 440/5-88-002) 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. 4 of 23 2017 Cass 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 in Cass Lake ranges from 6.5 to 9.2 feet (Figure 3). The annual means hover fairly close to the long-term mean. For trend analysis, see page 10. Transparency monitoring should be continued annually at site 210 in order to track water quality changes. Figure 3. Annual mean transparency compared to long-term mean transparency. Cass Lake transparency ranges from 5.5 to 21.0 feet at the primary site (Table 5). Figure 4 shows the seasonal transparency dynamics. The maximum Secchi reading is usually obtained in early summer. Cass Lake transparency is high in May and June, and then declines through August. The transparency then rebounds in October after fall turnover. This transparency dynamic is typical of a Minnesota lake. 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 that 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. 5 of 23 2017 Cass Lake Figure 4. Seasonal transparency dynamics from 2005-2015 (Site 210). The red line represents the seasonal 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. Cass Lake was rated as being "not quite crystal clear" 65% of the time by samplers between 1987 and 2015 (Figure 5). Physical Appearance Rating 10% 25% 25% Crystal clear water 65% Not quite crystal clear – a little algae visible 10% Definite algae – green, yellow, or brown color apparent 0% High algae levels with limited clarity and/or mild odor apparent 0% Severely high algae levels 65% Figure 5. Cass Lake physical appearance ratings by samplers. RMB Environmental Laboratories, Inc. 6 of 23 2017 Cass Lake As the Secchi depth decreases, the perception of recreational suitability of the lake decreases. Cass Lake was rated as having "minor aesthetic problems" 59% of the time between 1987 and 2015 (Figure 6).