Willow Creek IA 06-FLO-1829

from tributary in NE 1/4 S11 T93N R44W Plymouth Co. to headwaters.

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: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Stable
Created: 10/27/2025 3:11:09 PM
Updated: 1/30/2026 11:46:00 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2006	Class BWW1	Fish Kill: Due To Unknown Toxicity	Biological monitoring: Iowa DNR fish kill follow-up	New data: recovery of fish community from pollutant-caused fish kill

Documentation

Assessment Summary

The presumptive Class BWW1 use was "not assessed" based on 2024 fish kill follow-up sampling that indicated fish community recovery from the fish kill. According to IR fish kill follow-up methodology, the previous 5b fish kill impairment was de-listed. All other designated uses were "not assessed."

Assessment Explanation

Presumptive Class A1 - No Data

Presumptive Class BWW1 – Fish Kill Assessment:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/ Thermal	Fish per mile	47a REMAP 25 % fish per mile	>47a REMAP 25 % fish per mile?	47a expected fish taxa	Fish Taxa Present % (>50% to pass)
1532	07/31/2024	32.2	47a	MO/WW	1552	496	Yes (Pass)	7/10	70% (Pass)
The presumptive Class BWW1 use previously resided in Category 5b based on a fish kill that occurred in 2003. This segment’s fish community was sampled in 2024 as part of the DNR fish kill follow-up sampling program. The results from this follow-up sampling and comparison to ecoregion averages suggest that the fish community of this segment is similar to non-fish kill impacted streams. Based on the fish kill follow-up sampling results, the Category for the fish kill assessment was changed from 5b to 3a (not assessed).

Details about the 2003 fish kill can be found here: https://programs.iowadnr.gov/fishkill/Events/576

Monitoring and Methods

Assessment Key Dates

9/11/2003

Fish Kill

7/31/2024

Biological Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

150

Monitoring data more than 5 years old

330

Fish surveys