East Okoboji Lake IA 06-LSR-1652
Dickinson County S29T99NR36W at E edge of Okoboji
- 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 10:36:23 AM
- Updated
- 1/20/2022 8:57:06 AM
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. In addition, the Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms . The Class HH (fish consumption) use was assessed (evaluated) as “WINOFI” based on fish tissue sampling data. According to DNR’s assessment methodology, the one-time occurrence of a level of mercury above an advisory trigger level does not suggest impairment of the Class HH use. The Iowa DNR/DPH advisory protocol states that two consecutive samplings that show contaminant levels are above the trigger level in edible tissue are needed to justify issuance of an advisory. Additional monitoring will be conducted to better determine levels of mercury in the edible portions of fish in this lake.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2020 22300008 East
Okoboji Lake
Iowa DNR
FT See Below 84 East
Okoboji Lake
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 22300008 6 12 / 4 8 8.6 8.4 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 22300008 6 Chlorophyll a TSI 15 / 5 31 76 59 NO Monitored Full 22300008 6 Secchi TSI 15 / 5 43 73 59 NO Monitored Full 22300008 6 Total Phosphorus TSI 15 / 5 48 77 62 NA NA NA 22300008 6 Inorganic suspended solids 15 / 5 0.3 8 3 NA NA NA 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 22300008 6 Ammonia 12 / 4 0.0003 0.032 0.01 NA 0 / 0 4 NO Monitored Full 22300008 6 Dissolved Oxygen 13 / 5 6.6 12.9 8.5 0 NA / NA 4 NO Monitored Full 22300008 6 pH 12 / 4 8 8.6 8.4 0 NA / NA 4 NO Monitored Full 22300008 6 Temperature 13 / 5 15.7 27.4 22.4 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 22300008 6 6 276.54 99.7% 55.34 97.1% YES Evaluated 3b 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 - Fish Tissue Sampling:
Site ID Biopart Year Species # in sample / # of samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 84 tissue plug 2020 bluegill 10 18.7 0.086
84 fillet 2015 channel catfish 5 50.1 0.05 0.02 0.06 84 tissue plug 2020 crappie spp. 3 21.6 0.101
84 tissue plug 2019 largemouth bass 10 32.8 0.432
84 tissue plug 2017 largemouth bass 3 38.8 0.127
84 tissue plug 2020 muskie 3 93.1 0.568
84 tissue plug 2020 northern pike 18 75.5 0.171
84 tissue plug 2020 walleye 15 47.3 0.396
84 tissue plug 2019 walleye 5 53.2 0.221
84 tissue plug 2020 yellow perch 10 21.1 0.055
Support Level WINOFI The
Class HH (fish consumption) use was potentially impaired due to single sample
above an advisory threshold. Further monitoring is needed to confirm
impairment.