Assessment Summary
The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions as well as violations of the state’s pH criterion. The Class BLW use was assessed (monitored) as “not supported” due to violations of the state’s criterion for DO and pH. The Class BLW use was also assessed (evaluated) as “Winofi” due to a single non-pollutant fish kill. All other designated uses were “not assessed.”
Note: A TMDL for algae and turbidity at Swan Lake was prepared by DNR and approved by EPA in 2004. Because algal growth, turbidity, and pH Section 303(d) impairments are identified for the 2018 assessment/listing cycle are addressed by the TMDL, these impairments will be placed in IR Category 4a. However, the dissolved oxygen impairment is not addressed by the TMDL, this impairment will be placed in Category 5a of the current Integrated Report (i.e., Section 303(d) list).
Assessment Explanation
Data Sources:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site
Name
|
Site
Description
|
|
Iowa DNR
|
6
|
WQ
|
CY 2016-2020
|
22140001
|
Swan
Lake Max Depth
|
|
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
|
|
22140001
|
6
|
15 / 5
|
7.7
|
9.5
|
8.6
|
4
|
4
|
YES
|
Monitored
|
Not
|
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
|
|
22140001
|
6
|
Chlorophyll a TSI
|
15 / 5
|
26
|
74
|
59
|
NO
|
Monitored
|
Full
|
|
22140001
|
6
|
Secchi TSI
|
15 / 5
|
63
|
83
|
73
|
YES
|
Monitored
|
Not
|
|
22140001
|
6
|
Total Phosphorus TSI
|
15 / 5
|
58
|
88
|
85
|
NA
|
NA
|
NA
|
|
22140001
|
6
|
Inorganic suspended solids
|
15 / 5
|
0.4
|
9.6
|
3.8
|
NA
|
NA
|
NA
|
DNR's assessment methodology indicates that at least two
assessment/listing cycles with a TSI value less than or equal to 63 are
necessary to suggest de-listing of an impairment. The chlorophyll a
TSI value for the 2002 assessment listing cycle was 84, which based on DNR's
assessment/listing methodology indicated an impairment based on the narrative
criteria protecting against aesthetically objectionable conditions. Because the
TSI value for the 2020 assessment/listing cycle was less than the trigger of 65
(2020 listing for chlorophyll a was 63), and because the TSI value for the
current listing cycle is also 59, based on DNR's methodology, these values
suggest "full support" of the Class A1 uses protecting against
aesthetically objectionable conditions and the impairment (4a) for chlorophyll
a is suggested for delisting for the 2022 assessment/listing cycle.
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
|
|
22140001
|
6
|
Ammonia
|
15 / 5
|
0.0003
|
0.426
|
0.06
|
NA
|
0 / 0
|
4
|
NO
|
Monitored
|
Full
|
|
22140001
|
6
|
Dissolved Oxygen
|
14 / 5
|
4.4
|
14.8
|
8.5
|
3
|
NA / NA
|
4
|
NO
|
Monitored
|
Full
|
|
22140001
|
6
|
pH
|
15 / 5
|
7.7
|
9.5
|
8.6
|
4
|
NA / NA
|
4
|
YES
|
Monitored
|
Not
|
|
22140001
|
6
|
Temperature
|
15 / 5
|
13.4
|
27.2
|
22.3
|
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, Swan 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
|
|
22140001
|
6
|
6
|
163.30
|
88.6%
|
7.91
|
28.7%
|
NO
|
Evaluated
|
NA
|
Class BLW - Fish Kill:
The Class BLW use was assessed (evaluated) as “WINOFI”
due to fish kills that occurred in 2015. Because the cause of the fish kill was
not identified, or the fish kill was attributed to a non-pollutant cause (e.g.,
winterkill), the assessment type is “evaluated.” Segments assessed using
“evaluated” assessments are placed in Category 3b and are added to the state
list of waters in need of further investigation. If no additional fish kills
are reported in the segment for a 10 year period, the Category will be changed
from 3b to 3a (water not assessed).
Details about the 2015 fish kill can be found here:
https://programs.iowadnr.gov/fishkill/Events/893
Class HH - No Data
