Green Valley Lake IA 05-PLA-1472
Union County S26T73NR31W 2.5 mi NW of Creston.
The Class A1 use was assessed (monitored) as “not supported” due to algal and non-algal turbidity. The Class BLW use was assessed (monitored) as "not supported" due to violations of the Class BLW criterion for DO and "WINOFI" due to a large population of cyanobacteria. The Class C use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data. Note: A TMDL for algae, turbidity, and dissolved oxygen at Green Valley Lake was prepared by DNR and approved by EPA in 2019. Because all Section 303(d) impairments identified for the current assessment/listing cycle (algal growth, turbidity, and dissolved oxygen) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
Data
Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2018-2020 21880001 Green
Valley Beach (Green Valley State Park) Iowa DNR 6 WQ CY 2016-2020 22880001 Green
Valley Lake Iowa DNR 6 FT See Below 8 Green
Valley Lake N
of Creston
Class A1 - Indicator Bacteria: Site ID Data Source ID # Samples per Year (2018/ 2019/2020) 2018 Geometric Mean 2019 Geometric Mean 2020 Geometric Mean Violates Annual Geometric Mean? # 2018 SSM violations / SSM Violations needed for impairment # 2019 SSM violations / SSM Violations needed for impairment # 2020 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 21880001 6 8/14/5 19 14 18 NO 1 / 3 0 / 4 0 / NA NO Monitored Full 22880001 6 3/3/2 2 6 7 NO 0 / NA 0 / NA 0 / NA NO Evaluated Full Class A – 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 22880001 6 15 / 5 8 9.28 8.59 3 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 22880001 6 Chlorophyll a TSI 15 / 5 36 79 69 YES Monitored Not 22880001 6 Secchi TSI 15 / 5 56 83 73 YES Monitored Not 22880001 6 Total Phosphorus TSI 15 / 5 60 91 84 NA NA NA 22880001 6 Inorganic suspended solids 15 / 5 0.6 13 5.2 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 22880001 6 Ammonia 15 / 5 0.0003 0.1489 0.02 NA 0 / 0 4 NO Monitored Full 22880001 6 Dissolved Oxygen 15 / 5 2.1 13.8 7.6 3 NA / NA 4 NO Monitored Full 22880001 6 pH 15 / 5 8 9.28 8.59 3 NA / NA 4 NO Monitored Full 22880001 6 Temperature 15 / 5 17.6 26.5 23.6 0 NA / NA 4 NO Monitored Full According to DNR's methodology, a lake must meet water
quality standards for two consecutive cycles to suggest
de-listing. Therefore, Green Valley Lake will remain listed for the
2022 cycle as "not supported" its Class BLW uses due to dissolved
oxygen. 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 22880001 6 6 279.70 99.8% 138.45 97.8% YES Evaluated 3b Class C - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value Median Value # Violations Violates Significantly >10% Rule? Assessment Type Support Level 22880001 6 Inorganic nitrogen (nitrate and nitrite) 15 / 5 0.02 1.51 0.21 0.03 0 NO Monitored Full 22880001 6 pH 15 / 5 8 9.28 8.59 8.5 3 NO Monitored Full 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) 8 fillet 2011 channel catfish 3 51.3 0.054 0.03 0.09 8 tissue plug 2011 largemouth bass 4 33.5 0.2
Support Level Full
Additional Notes: A fishery
renovation was completed in 2008. Watershed improvements are being installed
and other a sediment removal project is scheduled for the winter of 2009/2010.
Water quality improvements are expected as this project progresses and the lake
is filled. Because of the water quality improvement project activities
throughout the assessment period, a limited number of samples were collected in
2008-2012.