East Okoboji Lake IA 06-LSR-1652
Dickinson County S29T99NR36W at E edge of Okoboji
- Cycle
- 2024
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 11/1/2023 8:13:34 AM
- Updated
- 12/27/2023 1:50:34 PM
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. The Class HH (fish consumption) use was assessed (monitored) as “not supported” 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 2018-2022 22300008 East
Okoboji Lake
Iowa DNR 6 FT See Below 1084 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 8.3 0 4 NO Mon 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 72 59 NO Mon Full 22300008 6 Secchi TSI 15 / 5 44 73 60 NO Mon Full 22300008 6 Total Phosphorus TSI 15 / 5 53 77 62 NA NA NA 22300008 6 Inorganic suspended solids 15 / 5 0.6 8 3 NA NA NA Class BLW - Binomial 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 Dissolved Oxygen 13 / 5 6.6 12.9 8.3 0 NA / NA 4 NO Mon Full 22300008 6 pH 12 / 4 8 8.6 8.3 0 NA / NA 4 NO Mon Full 22300008 6 Temperature 13 / 5 15.7 27.4 23 0 NA / NA 4 NO Mon 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 6 125.7558783 100% 3.065697552 21% NO Evaluated NA Class BLW - Toxic Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations >1 Acute / Chronic Violation Assessment Type Support Level 22300008 6 Ammonia 12 / 4 0.021 0.01 0.01 0 / 0 NO Mon Full 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) 1084 tissue plug 2020 bluegill 10 18.7 0.086
1084 fillet 2015 channel catfish 5 50.1 0.05 0.02 0.06 1084 tissue plug 2020 crappie spp. 3 21.6 0.101
1084 tissue plug 2019 largemouth bass 10 32.8 0.432
1084 tissue plug 2017 largemouth bass 3 38.8 0.127
1084 tissue plug 2021 muskie 7
0.596
1084 tissue plug 2020 muskie 3 93.1 0.568
1084 tissue plug 2021 northern pike 1
0.297
1084 tissue plug 2020 northern pike 18 75.5 0.171
1084 tissue plug 2020 walleye 15 47.3 0.396
1084 tissue plug 2019 walleye 5 53.2 0.221
1084 tissue plug 2021 yellow bass 9
0.106
1084 tissue plug 2020 yellow perch 10 21.1 0.055
Support Level Not A one meal/week mercury consumption advisory for muskie
exists on this segment. Walleye and largemouth bass results were also
elevated. Based on IR Methodology, the Class HH (fish consumption) use was
assessed as “not supported.”