Des Moines River IA 04-UDM-1220

from confluence with East Fork Des Moines R. (S19 T91N R28W Humboldt Co.) to Humboldt Dam at Lake Nokomis at Humboldt.

This is a DRAFT assessment

Draft assessments may change without notice

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2022 - 2024
Stream/River Water Quality Data	CY 2022 - 2024
Lake Water Quality Data	CY 2020 - 2024
Biological Sampling Data	CY 2020 - 2024*
Fish Kill Data	CY 2020 - 2024
Fish Tissue Sampling Data	CY 2020 - 2024
Continuous Dissolved Oxygen Sampling Data	CY 2020 - 2024
*Biological sites sampled in both 2019 and 2023 were also assessed.

Open Segment Map
View 2026 assessment summary page

Cycle: 2026
Current Phase: Public Comment
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Stable
Created: 10/27/2025 3:09:46 PM
Updated: 1/6/2026 2:09:20 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

Class HH

Human Health -

Not Supported

Fish Consumption Advisory: Mercury

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2014

Impairment Rationale

Fish consumption advisory in effect: no more than 1 meal/week

Data Source

Fish contaminant monitoring: Iowa DNR

TMDL Priority

Tier IV

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2008	Class A1	Bacteria: Indicator Bacteria- E. coli	Ambient monitoring: Iowa DNR-rivers	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed as "fully supported" based on indicator bacteria (E. coli) sampling data. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and on water quality monitoring data. The Class HH (fish consumption) use remains assessed as “not supported” due to the existence of a historic one meal per week mercury fish consumption advisory in this segment.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2022-2024	10460001	West Fork Des Moines River near Humboldt
Iowa DNR	6	BIO	See Below	933	West Fork Des Moines River	Humboldt

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

10460001

8/8/8

0 / 3

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
10460001	6	36 / 3	7.1	8.6	8.1	0	7	NO	MONITORED	FULL

Class BWW1 - 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
10460001	6	Chloride	36 / 3	12	100	36	NA	0 / 0	7	NO	MONITORED	FULL
10460001	6	Dissolved Oxygen	36 / 3	7.5	14.8	11.3	0	NA / NA	7	NO	MONITORED	FULL
10460001	6	pH	36 / 3	7.1	8.6	8.1	0	NA / NA	7	NO	MONITORED	FULL
10460001	6	Sulfate	36 / 3	23	180	101	0	NA / NA	7	NO	MONITORED	FULL
10460001	6	Temperature	36 / 3	0	26.9	11.8	0	NA / NA	7	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
10460001	6	Ammonia	36 / 3	0.39	0.07	0.02	0 / 0	NO	MONITORED	FULL
10460001	6	Cadmium	18 / 2	0.5	0.5	0.5	0 / 0	NO	MONITORED	FULL
10460001	6	Chromium	18 / 2	3	0.99	0.84	0 / 0	NO	MONITORED	FULL
10460001	6	Copper	18 / 2	2.1	1.3	1.4	0 / 0	NO	MONITORED	FULL
10460001	6	Lead	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10460001	6	Nickel	18 / 2	3.2	2	1.9	0 / 0	NO	MONITORED	FULL
10460001	6	Selenium	36 / 3	6	1.9	2	0 / 1	NO	MONITORED	FULL
10460001	6	Silver	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10460001	6	Zinc	18 / 2	3.8	0.8	0.5	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
933	10/2/24	2308	47b	MS	Floating Art Sub	66	Good	62	Pass
933	7/22/20	2308	47b	MS	Floating Art Sub	64	Good	62	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (2/2)	Full		Assessment was evaluated because the drainage area
Overall	Evaluated	Pass	Full	1	of the site was greater than the calibrated range.

Class BWW1- Continuous DO Monitoring:

Site ID	Data Source ID	# Days Monitoring (2016)	DO Criteria Type	# 2016 violations / Violations needed for impairment	Violates Annual Significantly >10% Rule?	Assessment Type	Support Level
			24 hr	0/6	No
933	6	29	16 hr	0/6	No	Evaluated	Full

Class HH - Fish Tissue: A historic one meal/week mercury consumption advisory existed on this segment. Based on IR Methodology, the Class HH (fish consumption) use was assessed as “not supported.”

Class HH-F - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	Number of Non - Detects	Mean Value > Criterion or MCL	Assessment Type	Support Level
10460001	6	Copper	18 / 2	2.1	1.3	1.4	5	NO	MONITORED	FULL
Site ID	Data Source ID	Parameter Name	# Samples per Year (2022/ 2023/2024)	2022 Mean	2023 Mean	2024 Mean	# Non-Detects per Year (2022/ 2023/2024)	Support Level per Year (2022/ 2023/2024)	Assessment Type	Support Level
10460001	6	Selenium	12/12/12	2.042	2.008	1.7	1/0/1	FS/FS/FS	MONITORED	FULL

Monitoring and Methods

Assessment Key Dates

7/22/2020

Biological Monitoring

1/5/2022

Monitoring Start

12/11/2024

Monitoring End

10/2/2024

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring