Cedar River IA 02-CED-479

from Rock Cr. nr Orchard (S24 T97N R17W Floyd Co.) to Iowa / Minnesota state line (S8 T100N R18W Mitchell Co.)

Assessment Cycle

2024

Release Status

Final

Data Collection Period

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Overall IR Category: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown

Created: 11/1/2023 8:12:25 AM
Updated: 2/2/2024 2:34:09 PM

Assessment conducted in accordance with Iowa's 2024 IR methodology

Use Support

Class A1

Recreation

Primary contact

Not Supported

Impairments

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2006

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Special project/study

Class BWW1

Aquatic Life

Warm Water Type 1

Fully Supported

Class HH

Human Health

Not Supported

Impairments

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2006

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

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "not supported" based on levels of indicator bacteria (E. coli) that exceeded Class A1 criteria. The Class BWW1 use was assessed as "fully supported" based on water quality monitoring data. The Class HH use was assessed as "not supported" based on the existence of a historic one meal per week mercury consumption advisory for any predator fish in this segment. Note: A TMDL for indicator bacteria was approved by EPA in February 2010 for this segment. The approval of this TMDL moved the bacterial impairment for this segment from Iowa's list of Section 303(d) waters (Category 5a of the IR) to IR Category 4a (impaired; TMDL not required).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
MNPCA	15	WQ	CY 2018-2020	99990099	Cedar River

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

99990099

0/9/6

255

184

YES

4 / 3

2 / NA

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
99990099	15	30 / 3	6.17	8.32	7.79	1	6	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
99990099	15	Dissolved Oxygen	30 / 3	7.3	12.5	8.9	0	NA / NA	6	NO	Monitored	Full
99990099	15	pH	30 / 3	6.17	8.32	7.79	1	NA / NA	6	NO	Monitored	Full
99990099	15	Temperature	30 / 3	2.6	24.6	17.9	0	NA / NA	6	NO	Monitored	Full

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

Monitoring and Methods

Assessment Key Dates

3/14/2018

Monitoring Start

9/29/2020

Monitoring End

2/1/2010

TMDL Completed

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

420

Indicator bacteria monitoring