Assessment Summary
The Class A1 use was assessed as "fully supported" based on indicator bacteria and pH monitoring. The Class BWW1 use was assessed as "WINOFI” based on biological sampling data and the occurrence of a single fish kill. The Class C (drinking water) use was assessed as "fully supported" based on water quality monitoring data. The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data.
Note: A TMDL for the nitrate impairment in this segment was approved by EPA in September 2009. The TMDL covered the nitrate impairment identified for this segment and the impairment remained in IR Category 4a (impaired; TMDL approved) until the 2022 IR cycle. However, the nitrate monitoring data collected since then has indicated "full support."
Assessment Explanation
Data Sources:
|
Data Source
|
Data Source ID
|
Data Type
|
Data Age
|
Site ID
|
Site
Name
|
Site
Description
|
|
USACE
|
12
|
WQ
|
CY 2022-2024
|
17770001
|
Des
Moines River at 66th. St.
|
|
|
USACE
|
12
|
FT
|
See Below
|
17770001
|
Des
Moines River at 66th. St.
|
|
|
Iowa DNR
|
6
|
BIO
|
See Below
|
917
|
Des
Moines River
|
Des
Moines – US1
|
Class A1 - Indicator Bacteria:
|
Site ID
|
Data Source ID
|
# Samples per Year (2022/ 2023/2024)
|
2022 Geometric Mean
|
2023 Geometric Mean
|
2024 Geometric Mean
|
Violates Annual Geometric Mean?
|
# 2022 SSM violations / SSM Violations needed for impairment
|
# 2023 SSM violations / SSM Violations needed for impairment
|
# 2024 SSM violations / SSM Violations needed for impairment
|
Violates Annual SSM Significantly >10% Rule?
|
Assessment Type
|
Support Level
|
|
17770001
|
12
|
10/10/10
|
16
|
23
|
12
|
NO
|
0 / 3
|
1 / 3
|
0 / 3
|
NO
|
MONITORED
|
FULL
|
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
|
|
17770001
|
12
|
67 / 3
|
7.81
|
9.01
|
8.21
|
1
|
11
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - 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
|
|
17770001
|
12
|
Dissolved Oxygen
|
67 / 3
|
8.15
|
15.46
|
11.13
|
0
|
NA / NA
|
11
|
NO
|
MONITORED
|
FULL
|
|
17770001
|
12
|
pH
|
67 / 3
|
7.81
|
9.01
|
8.21
|
1
|
NA / NA
|
11
|
NO
|
MONITORED
|
FULL
|
|
17770001
|
12
|
Temperature
|
67 / 3
|
1.4
|
29.4
|
17
|
0
|
NA / NA
|
11
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - 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
|
|
17770001
|
12
|
Ammonia
|
60 / 3
|
0.43
|
0.13
|
0.09
|
0 / 0
|
NO
|
MONITORED
|
FULL
|
Class BWW1 - Biological Sampling:
Benthic
Macroinvertebrates:
|
Site ID
|
Date
|
Drainage Area (mi2)
|
Ecoregion
|
Major Drainage
|
BM Sample Gear
|
BMIBI score
|
BMIBI Class
|
47b BMIBI BIT
|
BMIBI Pass/Fail
|
|
917
|
9/17/14
|
5840
|
47b
|
MS
|
Floating Art Sub
|
29
|
Poor
|
62
|
Fail
|
Overall:
|
Community
|
Assessment Type
|
Assessment Result
|
Support Level
|
IR Category
|
Reason
|
|
Benthic Macroinvertebrates
|
Evaluated
|
Fail (0/1)
|
WINOFI
|
|
Assessment was
evaluated because the drainage area
|
|
Overall
|
Evaluated
|
Fail
|
WINOFI
|
3bu
|
of the site is
greater than the calibrated range.
|
Class BWW1 - Fish kill Assessment:
A July 2024 fish kill
occurred in the Des Moines River immediately downriver from the Saylorville dam
that was caused by gas bubble trauma (GBT). Fish kills caused by GBT occur due
to a large imbalance between the concentrations of atmospheric gasses in the
water and the levels of these gasses dissolved in the blood of the fish. The
concentrations of dissolved gasses such as oxygen and nitrogen in river water
tend to equal the concentrations in the blood of a fish. When the levels of
atmospheric gasses dissolved in river water become very high (i.e.,
super-saturated)—such as can happen when water moves through or over a large
dam—the levels of these gasses will also rise in the blood of fish. As long as
fish can stay in deeper water, the hydrostatic (water) pressure will keep these
gasses fully dissolved in the fish’s blood. If, however, the flow of water
downstream from the dam is decreased suddenly, the depth of the water will also
decrease. With shallower water, fish are not able to move to deeper areas to
keep the hydrostatic pressure sufficiently high to keep the gasses fully
dissolved in their blood. During these conditions, the gasses dissolved in the
fish’s blood will gradually come out of solution as bubbles, and these bubbles
will interfere with blood circulation. Symptoms of gas bubble trauma in fish
include gas blisters on the skin at the margins of the scales and as pop-eye
(exophthalmia) where the eyes of the fish distend from the eye sockets. In the
extreme case, blood circulation is disrupted to the point that fish kills
occur.
The aquatic life use was placed in Category 3b (WINOFI list – potential impairment) because there weren’t multiple fish kills in this segment in the last five
years. Should additional GBT fish kills occur in this segment in the future,
the aquatic life use will be moved to IR Category 5b and be placed on the
Impaired Waters List.
Details about the 2024 fish kill can be found here: https://programs.iowadnr.gov/fishkill/events/1059
Class C
- Binomial 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
|
|
17770001
|
12
|
Inorganic nitrogen (nitrate and nitrite)
|
58 / 3
|
0.3
|
15.4
|
3.6
|
2.3
|
5
|
NO
|
MONITORED
|
FULL
|
|
17770001
|
12
|
pH
|
67 / 3
|
7.81
|
9.01
|
8.21
|
8.18
|
1
|
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)
|
|
17770001
|
whole
|
2016
|
common carp
|
5
|
NA
|
NA
|
0.03
|
<0.06
|
|
17770001
|
fillet
|
2016
|
largemouth bass
|
2
|
NA
|
0.11
|
|
|
|
Support Level
|
Full
|
Evaluated
|
|
|
|
|
|
|
