Beaver Creek IA 04-UDM-1233

mouth (S17 T79N R24W Polk Co.) to the Polk/Dallas county line (west line S18 T80N R25W Polk Co.

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: Declining
Trend Comment: New Class B ammonia and benthic macroinvertebrate impairments.
Created: 10/27/2025 3:09:46 PM
Updated: 1/14/2026 8:42:50 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

Not Supported

Biological: low aquatic macroinvertebrate IBI

Support Level

Not Supported

Impairment Code

5b-v - Biological - verified

Cause Magnitude

Moderate

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2026

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

TMDL Priority

Tier IV

Toxic Inorganics: Ammonia

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2026

Impairment Rationale

Violations of acute criterion

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier IV

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use was assessed as "not supported" due to levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW2 use was assessed as "not supported" based on violations of both the acute and chronic ammonia criteria and on biological sampling data.

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	10770001	Beaver Creek at Johnston
Polk CCB	29	WQ	CY 2022-2024	99990222	Beaver Creek
Polk CCB	29	WQ	CY 2022-2024	99990284	Beaver Creek
Polk CCB	29	WQ	CY 2022-2024	99990285	Beaver Creek
Polk CCB	29	WQ	CY 2022-2024	99990258	Beaver Creek
Polk CCB	29	WQ	CY 2022-2024	99990281	Beaver Creek
Iowa DNR	6	BIO	See Below	910	Beaver Creek	Johnston
Iowa DNR	6	BIO	See Below	1336	Beaver Creek	Grimes

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

10770001

8/8/8

791

189

562

YES

7 / 3

5 / 3

6 / 3

YES

MONITORED

NOT

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
10770001	6	36 / 3	7.3	8.5	8.2	0	7	NO	MONITORED	FULL

Class BWW2 - 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
10770001	6	Chloride	36 / 3	23	140	55	NA	0 / 0	7	NO	MONITORED	FULL
99990222	29	Chloride	6 / 2	33.61	124.58	73.61	NA	0 / 0	3	NO	EVALUATED	FULL
99990284	29	Chloride	6 / 2	16.48	52.76	36.81	NA	0 / 0	3	NO	EVALUATED	FULL
99990285	29	Chloride	6 / 2	24.67	99.35	53.68	NA	0 / 0	3	NO	EVALUATED	FULL
10770001	6	Dissolved Oxygen	36 / 3	7	15.7	10.9	0	NA / NA	7	NO	MONITORED	FULL
10770001	6	pH	36 / 3	7.3	8.5	8.2	0	NA / NA	7	NO	MONITORED	FULL
10770001	6	Sulfate	36 / 3	18	550	100	0	NA / NA	7	NO	MONITORED	FULL
99990222	29	Sulfate	6 / 2	29.12	396.36	131.85	0	NA / NA	3	NO	EVALUATED	FULL
99990284	29	Sulfate	6 / 2	13.74	37.81	29.76	0	NA / NA	3	NO	EVALUATED	FULL
99990285	29	Sulfate	6 / 2	19.52	313.74	98.43	0	NA / NA	3	NO	EVALUATED	FULL
10770001	6	Temperature	36 / 3	0	26.8	13.2	0	NA / NA	7	NO	MONITORED	FULL
99990222	29	Temperature	66 / 3	-0.56	31.11	13.66	0	NA / NA	11	NO	MONITORED	FULL
99990258	29	Temperature	47 / 3	0	26.67	14.65	0	NA / NA	8	NO	MONITORED	FULL
99990281	29	Temperature	53 / 3	4.44	33.33	18.66	2	NA / NA	9	NO	MONITORED	FULL
99990284	29	Temperature	6 / 3	13.33	22.22	18.52	0	NA / NA	3	NO	EVALUATED	FULL
99990285	29	Temperature	6 / 3	14.44	25	20.56	0	NA / NA	3	NO	EVALUATED	FULL

Class BWW2 - 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
10770001	6	Ammonia	36 / 3	6.6	0.4	0.02	1 / 1	YES	MONITORED	NOT
10770001	6	Cadmium	18 / 2	0.5	0.5	0.5	0 / 0	NO	MONITORED	FULL
10770001	6	Chromium	18 / 2	5	1.32	1	0 / 0	NO	MONITORED	FULL
10770001	6	Copper	18 / 2	5.3	2.2	1.7	0 / 0	NO	MONITORED	FULL
10770001	6	Lead	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10770001	6	Nickel	18 / 2	2.6	1.9	1.8	0 / 0	NO	MONITORED	FULL
10770001	6	Selenium	36 / 3	3.3	1.5	1.6	0 / 0	NO	MONITORED	FULL
10770001	6	Silver	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10770001	6	Zinc	18 / 2	7.9	2	1	0 / 0	NO	MONITORED	FULL

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	BM Sample Gear	BMIBI score	BMIBI Class	47b BMIBI BIT	BMIBI Pass/Fail
910	8/23/23	358.0	47b	MS/WW	Surber	54	Fair	62	Fail
1336	9/15/22	348.0	47b	MS/WW	ArtSub	39	Fair	62	Fail

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	Riffle Stream?	FIBI score	FIBI Class	47b FIBI BIT	FIBI Pass/Fail
1336	9/15/22	348.0	47b	MS/WW	No	45	Fair	32	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Monitored	Fail (0/2)	Not
Fish	Evaluated	Pass (1/1)	Full		Assessment was monitored because the two BMIBI samples used
Overall	Monitored	Fail	Not	5bv	for the assessment were collected in a recent five-year period.

Monitoring and Methods

Assessment Key Dates

2/9/2022

Monitoring Start

12/18/2024

Monitoring End

8/23/2023

Biological Monitoring

9/15/2022

Biological Monitoring

Methods

200

Physical/Chemical Monitoring

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys

420

Indicator bacteria monitoring

860

Other Agencies/Organizations provided monitoring data