Minnewashta Lake IA 06-LSR-1650
Dickinson County S29T99NR36W 2 mi. NNE of Milford.
- Cycle
- 2022
- Release Status
- Final
- Overall IR
- 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 1/4/2022 9:41:03 AM
- Updated
- 2/2/2022 2:56:40 PM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2018 | Class A1 | Algal Growth: Chlorophyll a | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 use was assessed (monitored) as “fully supported.” The Class BLW use was assessed (evaluated) as “WINOFI” due to an invasive species introduction (Zebra Mussels). The Class BLW use was also assessed (evaluated) as “WINOFI” based on the results of fish kill investigations. All other designated uses were “not assessed.”
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2020 22300011 Lake
Minnewashta
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 22300011 6 12 / 4 8 8.5 8.3 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 22300011 6 Chlorophyll a TSI 15 / 5 36 73 53 NO Monitored Full 22300011 6 Secchi TSI 15 / 5 41 70 59 NO Monitored Full 22300011 6 Total Phosphorus TSI 15 / 5 50 75 64 NA NA NA 22300011 6 Inorganic suspended solids 15 / 5 0.3 23.2 2.5 NA NA NA DNR's assessment methodology indicates that at least two
assessment/listing cycles with a TSI value less than or equal to 63 are
necessary to suggest de-listing of an impairment. The chlorophyll a
TSI value for the 2018 assessment listing cycle was 65, which based on DNR's
assessment/listing methodology indicated an impairment based on the narrative
criteria protecting against aesthetically objectionable conditions. Because the
TSI value for the 2020 assessment/listing cycle was less than the trigger of 65
(2020 listing for chlorophyll a was 59), and because the TSI value for the
current listing cycle is also 53, based on DNR's methodology, these values
suggest "full support" of the Class A1 uses protecting against
aesthetically objectionable conditions and the impairment (5a) for chlorophyll
a is suggested for delisting 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 22300011 6 Ammonia 12 / 4 0.0003 0.052 0.01 NA 0 / 0 4 NO Monitored Full 22300011 6 Dissolved Oxygen 13 / 5 6.5 12.4 8.6 0 NA / NA 4 NO Monitored Full 22300011 6 pH 12 / 4 8 8.5 8.3 0 NA / NA 4 NO Monitored Full 22300011 6 Temperature 13 / 5 15.9 28 22.7 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 22300011 6 6 107.32 99.8% 25.43 83.8% YES Evaluated WINOFI Class BLW - Fish Kill Assessment: The Class BLW aquatic life use assessment based on the 2020 fish kill placed this segment in Category 3b. This assessment was “evaluated” because: (1) the cause of the fish kill was not identified or (2) the fish kill was attributed to a non-pollutant cause (e.g., winterkill). Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of Waters In Need Of Further Investigation (WINOFI). If no additional fish kills are reported in this segment for a 10-year period (2030), the Category will be changed from 3b to 3a (not assessed). Details about the 2020 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/995 Class
BLW - Additional Information The
Class BLW use was assessed (evaluated) as “WINOFI” based on
information from the DNR Fisheries Bureau and results from the ISU lake
surveys. Based on information from the DNR Fisheries Bureau, 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