Swan Lake IA 04-RAC-1199

Carroll County S31T84NR34W 3 mi. SE of Carroll.

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.

Open Segment Map
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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: Eutrophic
Trend: Unknown
Created: 11/1/2023 8:13:11 AM
Updated: 2/5/2024 11:00:17 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity

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

2002

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

Low

Cycle Added

2024

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Algal Growth: Cyanobacteria

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

New

Source

Agriculture

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2018	Class BLW	Organic Enrichment: Low Dissolved Oxygen	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency and algal growth that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. All other designated uses were “not assessed.” Note: A TMDL for algae and turbidity at Swan Lake was prepared by DNR and approved by EPA in 2004. Because all of the Section 303(d) impairments identified for the current assessment/listing cycle are addressed by the TMDL, these impairments will be placed 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 2018-2022	22140001	Swan Lake Max 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
22140001	6	15 / 5	7.7	9.7	8.5	2	4	NO	Mon	Full

Swan Lake was assessed as "not supported" for the 2006 assessment/listing cycle due to frequent violations of the state Class A1 criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2024 assessment/listing cycle. Therefore, the (4a) impairment for pH is suggested for removal for the 2024 assessment/listing cycle.

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
22140001	6	Chlorophyll a TSI	15 / 5	26	80	65	YES	Mon	Not
22140001	6	Secchi TSI	15 / 5	62	87	73	YES	Mon	Not
22140001	6	Total Phosphorus TSI	15 / 5	58	98	86	NA	NA	NA
22140001	6	Inorganic suspended solids	15 / 5	0.6	9.6	3	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
22140001	6	Dissolved Oxygen	14 / 5	1.7	13.9	7.2	3	NA / NA	4	NO	Mon	Full
22140001	6	pH	15 / 5	7.7	9.7	8.5	2	NA / NA	4	NO	Mon	Full
22140001	6	Temperature	15 / 5	13.4	27.2	22.3	0	NA / NA	4	NO	Mon	Full

Swan Lake was assessed as "not supported" for the 2006 assessment/listing cycle due to frequent violations of the state Class BLW criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2024 assessment/listing cycle. Therefore, the (4a) impairment for pH is suggested for removal for the 2024 assessment/listing cycle.
Swan Lake was assessed as "not supported" for the 2018 assessment/listing cycle based on Dissolved Oxygen. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting. There were less than 10% of the samples exceeding the single-sample maximum criterion for the current assessment listing cycle. Therefore, the impairment for Dissolved Oxygen is suggested for delisting for the 2024 assessment/listing cycle.

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
22140001	6	5	292.01	100%	54.85	86%	YES	Evaluated	WINOFI

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
22140001	6	Ammonia	15 / 5	0.426	0.09	0.03	0 / 0	NO	Mon	Full

Class BLW - Fish Kill: The 3b fish kill was switched to 3a based on the age of the data and the lack of a second fish kill occurring within a 5 year period.

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/15/2018

Monitoring Start

8/30/2022

Monitoring End

12/14/2004

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)