Beaver Lake IA 04-RAC-1182

Dallas County S20T78NR29W 1.5 mi. N of Dexter.

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 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.

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Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 11/1/2023 8:13:11 AM
Updated: 2/5/2024 9:13:37 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

High

Cycle Added

2008

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

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

2022

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Exotic/Invasive Species: Fish Species

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Other: Exotic Species

Source Confidence

Moderate

Cycle Added

2018

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Algal Growth: Cyanobacteria

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

N/A

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

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

2022

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

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 the presence of aesthetically objectionable conditions caused by algae blooms that created low water clarity and violations of the state’s criterion for pH. The level of inorganic suspended solids was relatively low and does not suggest water quality problems due to non-algal turbidity. The Class BLW use was assessed (monitored) as “not supported” due to violations of the state’s criterion for pH and "WINOFI" based on information from the DNR Fisheries Bureau. All other designated uses are “not assessed.” Note: A TMDL for algae and pH in this lake was prepared and approved by EPA in October 2014. Because the primary Section 303(d) impairment identified for the current assessment/listing cycle (algae) is addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2022	22250001	Beaver Lake

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
22250001	6	15 / 5	7.77	9.51	8.61	4	4	YES	Mon	Not

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
22250001	6	Chlorophyll a TSI	15 / 5	40	78	70	YES	Mon	Not
22250001	6	Secchi TSI	15 / 5	49	81	68	YES	Mon	Not
22250001	6	Total Phosphorus TSI	15 / 5	57	82	71	NA	NA	NA
22250001	6	Inorganic suspended solids	15 / 5	0.6	142	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
22250001	6	Dissolved Oxygen	14 / 5	5	13	8	0	NA / NA	4	NO	Mon	Full
22250001	6	pH	15 / 5	7.77	9.51	8.61	4	NA / NA	4	YES	Mon	Not
22250001	6	Temperature	15 / 5	18.7	29.3	24.1	0	NA / NA	4	NO	Mon	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
22250001	6	5	268.3193624	100%	17.88309305	69%	YES	Evaluated	3b

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
22250001	6	Ammonia	15 / 5	0.5395	0.07	0.03	0 / 0	NO	Mon	Full

Class BLW - Fisheries Information:: The Class BLW (aquatic life) use was assessed (evaluated) as “WINOFI” based on information from the DNR Fisheries Bureau and results of the ISU lake surveys. Information from the DNR Fisheries Bureau suggests that Beaver Lake has no vegetation due to a large grass carp population and excessive algae and nutrients

Class HH - No Data: The previous assessment of full support has been removed due to the age of the data.

Monitoring and Methods

Assessment Key Dates

6/4/2018

Monitoring Start

9/19/2022

Monitoring End

10/31/2014

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)