Arbor Lake IA 03-NSK-864
Poweshiek County S20T80NR16W W edge of Grinnell
- Cycle
- 2022
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 12/22/2021 2:13:24 PM
- Updated
- 2/17/2022 10:11:13 AM
The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency and the presence of aesthetically objectionable conditions caused by algal blooms. The Class BLW use was assessed (monitored) as “fully supported”. All other designated uses were “not assessed.” Note: A TMDL for siltation and nutrients at Arbor Lake was prepared by DNR and approved by EPA in 2003. Because all Section 303(d) impairments identified in this assessment/listing cycle (algal growth, nutrients, and siltation) are addressed by the TMDL, Arbor Lake remains in IR Category 4a (TMDL approved).
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2019 22790004 Arbor
Lake Max Depth
Class A1 - Indicator Bacteria: No Data Class A1 - pH: Site ID Data Source ID # Samples / # Years Minimum Value Maximum Value Mean Value # Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22790004 6 12 / 4 7.4 8.6 8.2 0 4 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 22790004 6 Chlorophyll a TSI 12 / 4 26 70 64 NO Monitored Full 22790004 6 Secchi TSI 12 / 4 63 76 70 YES Monitored Not 22790004 6 Total Phosphorus TSI 12 / 4 67 78 72 NA NA NA 22790004 6 Inorganic suspended solids 12 / 4 5 56.5 11 NA NA NA Although the index value for Chlorophyll a is below the
impairment trigger of 65 for this assessment cycle, the Class A1 use of Arbor Lake remains "not supported" due to aesthetically objectionable
conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a
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 5). Therefore,
Arbor Lake will remain listed as "not supported" for the 2022
assessment/listing cycle. Class BLW - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value # Violations # Acute / Chronic Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22790004 6 Ammonia 12 / 4 0.0003 0.352 0.14 NA 0 / 0 4 NO Monitored Full 22790004 6 Dissolved Oxygen 12 / 4 4.5 13.5 9.7 1 NA / NA 4 NO Monitored Full 22790004 6 pH 12 / 4 7.4 8.6 8.2 0 NA / NA 4 NO Monitored Full 22790004 6 Temperature 12 / 4 20.1 28.1 23.9 0 NA / NA 4 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 Concentration = 75th Percentile Assessment Type Support Level 22790004 6 5 73.31 94.7% 12.64 64.0% NO Evaluated NA Class HH - No Data Note: Causes of impairments are attributed to multiple sources including Agriculture, Internal nutrient cycling (primarily lakes), Urban Runoff/Storm Sewers, and Naturals sources.