Lower Gar Lake IA 06-LSR-1646
Dickinson County S32T99NR36W 2 mi. NE of Milford.
- Cycle
- 2020
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Eutrophic
- Trend
- Improving
- Trend Comment
- Chlorophyll a TSI values are improving.
- Created
- 8/27/2020 2:24:08 PM
- Updated
- 10/15/2020 8:14:16 AM
The Class A1 uses are assessed (monitored) as “partially supported” due to aesthetically objectionable conditions caused by poor water transparency due primarily to high levels of non-algal turbidity and aesthetically objectionable conditions caused by algae blooms. The Class BLW uses are assessed (evaluated) as “partially supported” due to high levels of (inorganic) turbidity related primarily to sediment re-suspension at this shallow lake, due to an invasive species introduction (Zebra Mussels), and due to cyanobacteria blooms. All other designated uses are “not assessed.” Note: A TMDL for turbidity at Lower Gar Lake was prepared by DNR and approved by EPA in 2002. Because all Section 303(d) impairments identified for the current assessment/listing cycle [turbidity (algal and inorganic)] are addressed by the TMDL, this waterbody is placed in IR Category 4a.
Sources of
Data: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 WQ CY 2014-2018 22300012 Lower Gar Lake
Class A1 -
Indicator Bacteria: No Data Class A1 - pH: Site ID Data Source ID # Samples / # Years Maximum Value Mean Value Median Value # Violations % Violations Significantly >10% Violations Assessment Type Support Level 22300012 6 15 / 5 8.9 8.5 8.5 0 0% NO Monitored Full Class A1 - Lake
TSI's Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation Assessment Type Support Level 22300012 6 Chlorophyll a TSI 15 / 5 36 76 60 NO Monitored Full 22300012 6 Secchi TSI 15 / 5 55 78 64 NO Monitored Full 22300012 6 Total Phosphorus TSI 15 / 5 53 76 66 NA NA NA 22300012 6 Inorganic suspended solids 15 / 5 0.3 29.49 7 NA NA NA Although the
index values for Chlorophyll a and Secchi are below the impairment trigger of
65 for this assessment cycle, Lower Gar Lake was listed as partially supporting
its Class A1 uses due to aesthetically objectionable conditions. Based on
DNR's methodology, the median TSI values must be 63 or less for two
consecutive assessment/listing cycles before a lake can be removed from the
state's Section 303(d) list (IR Category 4a). Therefore, Lower Gar
Lakewill remain listed as "not supported" for the 2020
assessment/listing cycle. Class BLW -
Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations % Acute/ Chronic Violations Significantly >10% Violations Assessment Type Support Level 22300012 6 Ammonia 15 / 5 0.107 0.02 0.01 0 / 0 0% / 0% NO Monitored Full 22300012 6 Dissolved oxygen 15 / 5 17.4 10.4 9.8 NA / 0 NA / 0% NO Monitored Full 22300012 6 pH 15 / 5 8.9 8.5 8.5 0 / NA 0% / NA NO Monitored Full 22300012 6 Temperature 15 / 5 28.1 23.3 23.3 0 / 0 0% / 0% NO Monitored Full Class BLW -
Lake Planktonic Cyanobacteria: Site ID Data Source ID # Samples Maximum Cyanobacteria Wet Mass Maximum Cyanobacteria % Composition Median Cyanobacteria Wet Mass Median Cyanobacteria % Composition Median Cyanobacteria Wet Mass = 75th
Percentile Assessment Type Support Level 22300012 6 11 204.081 99.8 % 31.572 66.5 % YES Evaluated 3b Class BLW additional information: This lake was infested with Zebra mussels in 2012 and the population exploded in 2015. This invasive species will likely cause water quality to degrade in the future. This potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation. Class HH - No Data