Lake Orient IA 05-NOD-1396

Adair County S20T74NR31W approx 1 mi SW of Orient.

Assessment Cycle

2024

Release Status

Final

Data Collection Period

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.

Overall IR Category: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Stable

Created: 11/1/2023 8:13:21 AM
Updated: 12/22/2023 1:29:51 PM

Assessment conducted in accordance with Iowa's 2024 IR methodology

Use Support

Class A1

Recreation

Primary contact

Not Supported

Impairments

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Moderate

Cycle Added

2002

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

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

TMDL monitoring: Iowa DNR

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

TMDL monitoring: Iowa DNR

Class BLW

Aquatic Life

Lakes and wetlands

Not Supported

Impairments

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

TMDL monitoring: Iowa DNR

Further Investigation Needed

Support Level

Water in Need of Further Investigation (WINOFI)

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

Class C

Drinking Water

Not Supported

Impairments

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

New

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2024

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 aesthetically objectionable conditions caused by poor water clarity due to non-algal turbidity and algal turbidity. Violations of the Class A1 criterion for pH also contributed to impairment at this lake. The Class BLW use was assessed (monitored) as “not supported” due to violations of the Class BLW criterion for pH. The Class BLW use was also assessed (evaluated) as “WINOFI” due to cyanobacteria algae blooms. The Class C was assessed (monitored) as “not supported” due to violations of the Class BLW criterion for pH. All other designated uses were “not assessed.” Note: A TMDL for algae and pH at Orient Lake was prepared by DNR and approved by EPA in October 2020. Additionally, a TMDL for siltation at Orient Lake was prepared by DNR and approved by EPA in 2001. Because all Section 303(d) impairments are identified for the current assessment/listing cycle are addressed by the TMDL, this waterbody is placed in 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	22010002	Lake Orient

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
22010002	6	15 / 5	7.8	9.8	8.8	5	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
22010002	6	Chlorophyll a TSI	15 / 5	49	94	73	YES	Mon	Not
22010002	6	Secchi TSI	15 / 5	56	93	73	YES	Mon	Not
22010002	6	Total Phosphorus TSI	15 / 5	65	114	96	NA	NA	NA
22010002	6	Inorganic suspended solids	15 / 5	0.7	26	10.5	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
22010002	6	Dissolved Oxygen	15 / 5	5.9	11.6	8.7	0	NA / NA	4	NO	Mon	Full
22010002	6	pH	15 / 5	7.8	9.8	8.8	5	NA / NA	4	YES	Mon	Not
22010002	6	Temperature	15 / 5	20.1	30	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
22010002	6	6	309.9187487	99%	15.99193403	53%	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
22010002	6	Ammonia	15 / 5	0.6903	0.09	0.04	0 / 0	NO	Mon	Full

Class C - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22010002	6	Inorganic nitrogen (nitrate and nitrite)	14 / 5	0.02	2.95	0.62	0.17	0	NO	Mon	Full
22010002	6	pH	15 / 5	7.8	9.8	8.8	8.8	5	YES	Mon	Not

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

6/5/2018

Monitoring Start

9/21/2022

Monitoring End

8/28/2001

TMDL Completed

10/30/2020

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)