| Report Year: 2009 |
| Clear Lake, Cerro Gordo County |
| Summary Data Table |
| Parameter | 6/25/2009 | 7/30/2009 | 2009 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 |
| Lake Depth (m) | 5.5 | 5.5 | 5.5 | 5.5 | 5.4 | 4.7 | 5.2 | 5.2 | 5.1 | 5.3 | 5.1 |
| Thermocline Depth (m) | Nil | Nil | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| Secchi Disk Depth (m) | 0.7 | 0.5 | 0.6 | 1.2 | 0.5 | 0.5 | 0.5 | 1.4 | 0.8 | 0.7 | 0.4 |
| Temperature(oC) | 24.2 | 23.3 | 23.7 | 23.8 | 23.5 | 25.1 | 23.3 | 22.8 | 24.2 | 23.3 | 23.9 |
| Dissolved Oxygen (mg/L) | 8.6 | 7.3 | 8.0 | 7.1 | 10.0 | 7.6 | 10.9 | 10.4 | 9.2 | 7.6 | 9.2 |
| Dissolved Oxygen Saturation (%) | 103 | 86 | 94.2 | 84.9 | 116.6 | 92.5 | 128.1 | 121.5 | 109.8 | 95.9 | 108.5 |
| Specific Conductivity (μS/cm) | 370.0 | 410.0 | 390.0 | 365.0 | 346.3 | 343.3 | 385.2 | 343.4 | 406.3 | 259.6 | 293.9 |
| Turbidity (NTU) | 9.3 | 6.6 | 7.9 | 11.9 | 16.3 | 90.3 | 83.1 | 16.6 | 55.8 | 38.2 | 164.6 |
| Chlorophyll a (μg/L) | 13.0 | 12.0 | 12.5 | 22.4 | 53.1 | 82.0 | 81.5 | 20.7 | 30.2 | 70.7 | 30.8 |
| Total Phosphorus as P (μg/L) | 35 | 50 | 43 | 47 | 70 | 92 | 77 | 67 | 62 | 103 | 140 |
| SRP as P (μg/L) | 1 | - | 1 | - | 1 | - | 1 | 4 | 1 | - | - |
| Total Nitrogen as N (mg/L) | 1.42 | 1.39 | 1.41 | 1.07 | 1.77 | 1.57 | 1.60 | 1.55 | 1.22 | 1.83 | 1.97 |
| (Phenate)Ammonia Nitrogen (NH3 + NH4+) as N (μg/L) | 16 | 16 | 16 | 163 | 16 | 54 | 26 | - | - | - | - |
| (Phenate)Ammonia Nitrogen (NH3) as N (un-ionized)(μg/L) | 1.3 | 2.2 | 1.7 | 6.6 | 1.0 | 6.2 | 7.2 | - | - | - | - |
| Nitrate + Nitrite (NO3 + NO2) as N (mg/L) | 0.29 | 0.12 | 0.16 | 0.15 | 0.12 | 0.15 | 0.31 | 0.19 | 0.20 | 0.24 | 0.17 |
| TN:TP ratio | 41 | 28 | 34 | 31 | 25 | 18 | 20 | 24 | 22 | 18 | 18 |
| pH | 8.8 | 8.8 | 8.8 | 8.3 | 8.4 | 8.4 | 8.9 | 8.3 | 8.5 | 8.5 | 7.4 |
| Alkalinity as CaCO3 (mg/L) | 163 | 144 | 154 | 170 | 152 | 149 | 125 | 110 | 157 | 129 | 149 |
| Silica as Si (mg/L) | - | - | - | - | - | 8.06 | 3.43 | 4.93 | 5.85 | - | - |
| Dissolved Organic Carbon (mg/L) | 8.48 | 8.61 | 8.55 | 7.84 | 9.14 | 9.74 | 9.37 | 12.75 | 12.44 | - | - |
| Inorganic Suspended Solids (mg/L) | 12 | 3 | 7 | 4 | 8 | 12 | 7 | 8 | 7 | 11 | 19 |
| Volatile Suspended Solids (mg/L) | - | 11 | 11 | 9 | 15 | 20 | 14 | 10 | 11 | 17 | 28 |
| Total Suspended Solids (mg/L) | 12 | 13 | 13 | 13 | 23 | 32 | 21 | 19 | 18 | 28 | 47 |
| Carlson Trophic State Index (Secchi)* | 65 | 70 | 67 | 58 | 70 | 72 | 70 | 55 | 64 | 66 | 73 |
| Carlson Trophic State Index (Chl a)* | 56 | 55 | 55 | 61 | 70 | 74 | 74 | 60 | 64 | 72 | 64 |
| Carlson Trophic State Index (TP)* | 55 | 61 | 58 | 60 | 65 | 69 | 67 | 65 | 64 | 71 | 75 |
| *Index values generally range between 0 and 100, with increasing values indicating more eutrophic conditions. |