Don Williams Lake IA 04-UDM-1249

Boone County S5T84NR27W 5 mi. N of Ogden.

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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Stable
Created: 10/27/2025 3:10:04 PM
Updated: 11/20/2025 8:04:18 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Slight

Status

New

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2026

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Sedimentation/Siltation

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2004

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by non-algal turbidity and algal blooms. The Class BLW use was assessed (evaluated) as “not supported” due to siltation impacts, especially in the upper portions of the lake. All other designated uses are “not assessed.” Note: A TMDL for organic enrichment and siltation at Don Williams Lake was prepared by DNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the current assessment/listing cycle are addressed by the TMDL, this waterbody remains in IR Category 4a.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2020-2024	22080004	Don Williams Lake (maximum water depth)

Class A1 - Indicator Bacteria: No Data

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
22080004	6	15 / 5	7.4	9.1	8.2	2	4	NO	MONITORED	FULL

Class A1 - Lake TSI's

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation?	Assessment Type	Support Level
22080004	6	Chlorophyll a TSI	15 / 5	50	75	68	YES	MONITORED	NOT
22080004	6	Secchi TSI	15 / 5	49	73	67	YES	MONITORED	NOT
22080004	6	Total Phosphorus TSI	15 / 5	37	96	65	NA	NA	NA
22080004	6	Fixed suspended solids	15 / 5	0.7	26	2	NA	NA	NA

Class BLW - 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
22080004	6	Dissolved Oxygen	14 / 5	3.4	15.8	9.7	1	NA / NA	4	NO	MONITORED	FULL
22080004	6	pH	15 / 5	7.4	9.1	8.2	2	NA / NA	4	NO	MONITORED	FULL
22080004	6	Temperature	15 / 5	16.2	27.8	22.7	0	NA / NA	4	NO	MONITORED	FULL

Class BLW - Lake Planktonic Cyanobacteria:

Site ID	Data Source ID	# Samples	Maximum Cyanobacteria Wet Mass	Maximum Cyanobacteria % Composition	Median Cyanobacteria Wet Mass	Median Cyanobacteria % Composition	Median Cyanobacteria Concentration = 75th Percentile	Assessment Type	Support Level
22080004	6	5	8.8881	68.99%	4.8725	12.31%	NO	EVALUATED	NA

Class BLW - 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
22080004	6	Ammonia	15 / 5	0.319	0.07	0.04	0 / 0	NO	MONITORED	FULL

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/27/2020

Monitoring Start

9/4/2024

Monitoring End

3/10/2005

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)