Carter Lake IA 06-WEM-1714

Pottawattamie County S23T75NR44W at Carter Lake.

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: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:13:38 AM
Updated: 2/5/2024 1:36:25 PM

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

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2022

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

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2024

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Organic Enrichment: Low Dissolved Oxygen

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

N/A

TMDL Priority

Tier II

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

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

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

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "not supported" due primarily to high levels of algal and non-algal turbidity that reduce water transparency and create 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/algal toxins, chlorophyll a, total phosphorus, total nitrogen, and pH at Carter Lake was prepared by DNR and the Nebraska Department of Environmental Management and approved by EPA in 2007. Because all Section 303(d) impairments identified for the current assessment/listing cycle (pH) are addressed by the TMDL, this waterbody remains 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	22780001	Carter 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
22780001	6	12 / 4	7.4	8.5	8	0	4	NO	Mon	Full

Carter Lake was assessed as "not supported" for the 2018 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
22780001	6	Chlorophyll a TSI	12 / 4	45	83	68	YES	Mon	Not
22780001	6	Secchi TSI	12 / 4	67	83	74	YES	Mon	Not
22780001	6	Total Phosphorus TSI	12 / 4	62	81	72	NA	NA	NA
22780001	6	Inorganic suspended solids	12 / 4	0.6	41	12.5	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
22780001	6	Dissolved Oxygen	12 / 4	1.8	9.7	6	4	NA / NA	4	YES	Mon	Not
22780001	6	pH	12 / 4	7.4	8.5	8	0	NA / NA	4	NO	Mon	Full
22780001	6	Temperature	12 / 4	20.6	29.2	24.5	0	NA / NA	4	NO	Mon	Full

Carter Lake was assessed as "not supported" for the 2018 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 on 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 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
22780001	6	4	53.78477186	86%	19.59145509	63%	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
22780001	6	Ammonia	12 / 4	0.057	0.02	0.02	0 / 0	NO	Mon	Full

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

6/4/2018

Monitoring Start

9/19/2022

Monitoring End

8/30/2007

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)