Iowa DNR
Iowa DNR
ADBNet
Water Quality Assessments
Impaired Waters List

Willow Creek IA 06-LSR-1626

mouth (S17 T94N R36W Clay Co.) to confluence with unnamed tributary in NW 1/4 S31 T95N R37W Clay Co.

Cycle
2024
Release Status
Final
Overall IR
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Unknown
Created
11/1/2023 8:13:21 AM
Updated
2/6/2024 9:05:57 AM
Use Support
Class A1
Recreation - Primary contact
Not Supported
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
Low
Cycle Added
2012
Impairment Rationale
Geometric mean criterion exceeded
Data Source
TMDL monitoring: Iowa DNR
TMDL Priority
Tier III
Class BWW2
Aquatic Life - Warm Water Type 2
Not Supported
Support Level
Not Supported
Impairment Code
5b-t - Biological - tentative
Cause Magnitude
Moderate
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2004
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
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 violations of the state water quality criteria for indicator bacteria. The Class BWW2 use was assessed as “not supported” based 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 2010

11210003

Willow Creek near Royal

Iowa DNR

6

BIO/WQ

See Below

306

Willow Creek

Rossie – REMAP #31


Presumptive Class A1 - Indicator Bacteria: 2010

Site ID

Data Source ID

# Samples / # Years

2010 Geometric Mean

Annual Geometric Mean Violation

# Violations

% Violations

Significantly >10% Violations

Assessment Type

Support Level

11210003

6

12 / 1

1113

Yes

10

77%

Yes

Evaluated

Not


Class BWW2 - Biological Sampling:


Benthic Macroinvertebrates:

BioNet Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage

BM Sample Gear

BMIBI score

BMIBI Class

47a BMIBI BIT

BMIBI Pass/Fail

306

8/1/18

51

47a

MO

Hess

22

Poor

54

Fail


Fish:

BioNet Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage

Riffle Stream?

FIBI score

FIBI Class

47a FIBI BIT

FIBI Pass/Fail

306

8/1/18

51

47a

MO

NA

41

Fair

43

Pass*


Overall:

Community

Assessment Type

Assessment Result

Support Level

IR Category

Reason

Benthic Macroinvertebrates

Evaluated

Fail (0/1)

Not

Fish

Evaluated

Pass (1/1)

Full

Overall

Evaluated

Fail

Not

5bt

Assessment was evaluated because it was based on a single sample.


Class BWW2 - Continuous DO Monitoring: 2018

Site ID

Data Source ID

# Days Monitoring (2018)

DO Criteria Type

# 2018 violations / Violations needed for impairment

Violates Annual Significantly >10% Rule?

Assessment Type

Support Level

24 hr

0/4

No

306

6

14

16 hr

0/4

No

Evaluated

Full

Monitoring and Methods
Assessment Key Dates
3/9/2010
Monitoring Start
11/1/2010
Monitoring End
8/1/2018
Biological Monitoring
7/18/2018
Monitoring Start
8/1/2018
Monitoring End
Methods
150
Monitoring data more than 5 years old
315
Regional reference site approach
320
Benthic macroinvertebrate surveys
330
Fish surveys
420
Indicator bacteria monitoring