West Swan Lake IA 04-UDM-1754
Emmet County S31T99NR32W 3 mi. SE of Gruver.
- Cycle
- 2024
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 11/14/2023 3:02:13 PM
- Updated
- 1/4/2024 8:05:46 AM
The Class BLW use was assessed as "not supported" due to high levels of total suspended solids that leads to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life. High levels of algae at this shallow lake also suggest impairment due to aesthetically objectionable conditions. 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 2018-2020 29320002 West
Swan Lake (center)-Emmet-2
Class BLW – Shallow Lake TSI: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation? Assessment Type Support Level 29320002 6 Chlorophyll a TSI 14 / 3 53 83 69 YES Mon Not The TSI value for Secchi depth is not used to evaluate the
attainment of the aquatic life use in shallow lakes. Due to the depth of these
shallow lakes, TSI values for Secchi depth can be misleading. In some
instances, the Secchi disk remains visible at the bottom of the lake and the
depth of the lake is recorded as the Secchi depth. In these instances, water
clarity may be sufficient to support the Class BLW use, but the index value is
limited by the depth of the lake. Thus, the combination of total suspended
solids and chlorophyll a was used to determine whether or not the Class BLW use
was impaired in these shallow systems. 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 29320002 6 Dissolved Oxygen 15 / 3 4.05 13.86 9.41 2 NA / NA 4 NO Mon Full 29320002 6 pH 10 / 2 7.85 8.89 8.45 0 NA / NA 3 NO Mon Full 29320002 6 Temperature 15 / 3 12.8 29.5 21.8 0 NA / NA 4 NO Mon Full Class BLW - Protection of Submerged Aquatic Vegetation: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median Value >= SAV Assessment Type Support Level 29320002 6 Total suspended solids 14 / 3 12 62 32 Yes Mon Not Guidelines for wetland assessment from the Upper Mississippi
River Conservation Committee’s Water Quality Technical Section (2003) state
that a median total suspended solids concentration during the growing season of
less than 30 mg/L is necessary to provide sufficient water clarity to support
the growth of submersed aquatic vegetation (SAV) in wetlands and shallow lakes.
High levels of total suspended solids impede the growth of SAV. SAV is critical
to the health of wetland and shallow lake ecosystems. The elimination of SAV
can degrade habitat quality such that undesirable aquatic species such as
cyanobacteria, common carp and fathead minnows dominate. As such, the
suppression of SAV constitutes a violation of Iowa’s narrative water quality
criteria protecting against undesirable or nuisance aquatic life.
Class HH - No Data Additional
information:
Additional monitoring of
fish and aquatic vegetation populations at West Swan Lake by DNR staff also
suggests that the high levels of total suspended solids and algae have adverse
effects on fish populations and limit the production of rooted aquatic
vegetation in this wetland. These results further indicate that the aquatic
life uses of this wetland should be assessed as "not supported."