Brushy Creek Lake IA 04-UDM-1276

Webster Co. in S34 T88N R27W; 5 miles E. of Lehigh

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 3:10:05 PM
Updated: 11/24/2025 2:30:34 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

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

2012

Impairment Rationale

Single-sample maximum criterion exceeded in significantly > 10% of samples

Data Source

TMDL monitoring: Iowa DNR

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Exotic/Invasive Species

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Class HH

Human Health -

WINOFI

Metals: Mercury

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Atmospheric Deposition

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Potential Impairment

Data Source

Fish contaminant monitoring: Iowa DNR

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to violations of the state's indicator bacteria criteria. The Class BLW use was assessed (evaluated) as “WINOFI” due to invasive species. The Class HH use was assessed as “WINOFI” based on fish tissue 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	21940001	Brushy Creek Beach
Iowa DNR	6	WQ	CY 2020-2024	22940002	Brushy Creek Lake
Iowa DNR	6	FT	See Below	1283	Brushy Creek Lake

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

21940001

13/13/13

4 / 4

2 / 4

0 / 4

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
21940001	6	45 / 3	7.8	9.2	8.4	3	8	NO	MONITORED	FULL
22940002	6	18 / 5	7.8	8.9	8.4	0	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
22940002	6	Chlorophyll a TSI	18 / 5	30	78	63	NO	MONITORED	FULL
22940002	6	Secchi TSI	18 / 5	28	72	60	NO	MONITORED	FULL
22940002	6	Total Phosphorus TSI	18 / 5	35	70	59	NA	NA	NA
22940002	6	Fixed suspended solids	18 / 5	0.7	12	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
21940001	6	Dissolved Oxygen	45 / 3	5.23	17.79	9.99	0	NA / NA	8	NO	MONITORED	FULL
22940002	6	Dissolved Oxygen	16 / 5	6.4	18.1	10.5	0	NA / NA	4	NO	MONITORED	FULL
21940001	6	pH	45 / 3	7.8	9.2	8.4	3	NA / NA	8	NO	MONITORED	FULL
22940002	6	pH	18 / 5	7.8	8.9	8.4	0	NA / NA	4	NO	MONITORED	FULL
21940001	6	Temperature	45 / 3	16.509	27.909	24.075	0	NA / NA	8	NO	MONITORED	FULL
22940002	6	Temperature	18 / 5	11.4	29.1	21.4	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
22940002	6	6	6.310479599	86.01%	1.777580394	33.78%	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
22940002	6	Ammonia	18 / 5	0.29	0.07	0.02	0 / 0	NO	MONITORED	FULL

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
1283	fillet	2013	channel catfish	3	49.3	0.05	<0.2	<0.6
1283	tissue plug	2016	largemouth bass	5	38.6	0.05
1283	tissue plug	2021	muskie	1		0.368
Support Level	WINOFI

Additional Information:

The Class B(LW) (aquatic life) use was assessed (evaluated) as “not supported” based on information from the DNR Fisheries Bureau and results from the ISU lake surveys. Information from the DNR Fisheries Bureau indicated this lake had excessive growth of curly-leaf pondweed and brittle naiad. Additionally, Zebra mussel veligers were recently discovered in the lake.

Monitoring and Methods

Assessment Key Dates

5/19/2020

Monitoring Start

10/22/2020

Monitoring End

8/29/2013

Fish Tissue Monitoring

8/30/2016

Fish Tissue Monitoring

4/9/2021

Fish Tissue Monitoring

4/6/2022

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring