Assessment Summary
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 that lead to impairment due to aesthetically objectionable conditions, and violations of the class BLW criteria for pH. All other designated uses were “not assessed.”
Assessment Explanation
Data Sources:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site
Name
|
Site
Description
|
|
Iowa DNR
|
6
|
WQ
|
CY 2019-2022
|
22300022
|
Swan
Lake
|
|
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
|
|
22300022
|
6
|
Chlorophyll a TSI
|
9 / 3
|
51
|
82
|
70
|
YES
|
Evaluated
|
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
|
|
22300022
|
6
|
Dissolved Oxygen
|
9 / 3
|
8.12
|
16.21
|
11.03
|
0
|
NA / NA
|
3
|
NO
|
Mon
|
Full
|
|
22300022
|
6
|
pH
|
7 / 2
|
8.24
|
9.91
|
8.98
|
3
|
NA / NA
|
3
|
YES
|
Mon
|
Not
|
|
22300022
|
6
|
Temperature
|
9 / 3
|
12.5
|
32.4
|
21.9
|
1
|
NA / NA
|
3
|
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
|
|
22300022
|
6
|
Total suspended solids
|
9 / 3
|
1
|
290
|
26
|
NO
|
Evaluated
|
Full
|
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.
DNR's assessment methodology indicates that a median growing season total suspended solids concentration of 30 mg/L with at least 10 samples collected over 3 years is needed to suggest de-listing of the SAV impairment. While the assessment suggests "full support", the data quantity requirement has not been met for a monitored assessment.Therefore, Swan Lakewill remain listed as "not supported" for the 2024 assessment/listing cycle.
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
|
|
22300022
|
6
|
Ammonia
|
7 / 2
|
0.14
|
0.07
|
0.02
|
0 / 0
|
NO
|
Evaluated
|
Full
|
Class HH - No Data
