Lake Keomah IA 03-SSK-930

Mahaska County S13T75NR15W 4.5 mi E of Oskaloosa.

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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

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Cycle: 2022
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/27/2021 9:27:46 AM
Updated: 1/5/2022 10:23:16 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Beach monitoring: Iowa DNR WQMA

TMDL Priority

Tier II

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Slight

Status

New

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2022

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

2022

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Not Supported

Fish Consumption Advisory: Mercury

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2012

Impairment Rationale

Fish consumption advisory in effect: no more than 1 meal/week

Data Source

Fish contaminant monitoring: Iowa DNR

TMDL Priority

Tier IV

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as “not supported” due to levels of indicator bacteria (IR 5a) and "not supported” due to poor water transparency caused by non-algal turbidity (IR 4a). The Class BLW use was assessed as “WINOFI” based on cyanobacteria blooms. The Class C use was assessed as “fully supported” based on water quality monitoring data. The Class HH (fish consumption) use remains assessed as "not supported" based on fish tissue sampling data and due to the existence of a fish consumption advisory at this lake (IR 5a). Note: A TMDL for siltation at Lake Keomah was prepared by DNR and approved by EPA in 2002. In September 2012, DNR received EPA approval of a TMDL for the impairments of the Class A1 and Class BLW uses caused by algae and pH. Not all of the section 303(d) impairments identified for the current (2018) assessment/listing cycle (indicator bacteria, mercury), however, are addressed in the TMDL. Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the current assessment/listing cycle.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2020	21620001	Lake Keomah Beach (Lake Keomah State Park)
Iowa DNR	6	WQ	CY 2016-2020	22620002	Lake Keomah	Lake Deep Point
Iowa DNR	6	FT	See Below	168	Lake Keomah	Near Oskaloosa

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

21620001

13/15/15

103

2 / 4

4 / 4

3 / 4

YES

Monitored

Not

22620002

3/3/3

0 / NA

Evaluated

Full

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
22620002	6	15 / 5	7.4	9.2	8.5	2	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
22620002	6	Chlorophyll a TSI	15 / 5	37	78	62	NO	Monitored	Full
22620002	6	Secchi TSI	15 / 5	44	81	73	YES	Monitored	Not
22620002	6	Total Phosphorus TSI	15 / 5	50	80	72	NA	NA	NA
22620002	6	Inorganic suspended solids	15 / 5	0.3	18	3.2	NA	NA	NA

DNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment. The Secchi depth TSI value for the 2016 assessment listing cycle was 65, which based on DNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions.Because the TSI value for the 2020 assessment/listing cycle was less than the trigger of 65 (2020 listing for Secchi depth a was 63), and because the TSI value for the current listing cycle is also 62, based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (5a) for Secchi depth is suggested for delisting for the 2022 assessment/listing cycle.

Class BLW - Conventional 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
22620002	6	Ammonia	15 / 5	0.0003	0.5801	0.1	NA	0 / 0	4	NO	Monitored	Full
22620002	6	Dissolved Oxygen	14 / 5	5.1	13.4	9.2	0	NA / NA	4	NO	Monitored	Full
22620002	6	pH	15 / 5	7.4	9.2	8.5	2	NA / NA	4	NO	Monitored	Full
22620002	6	Temperature	15 / 5	20.2	29.7	24.7	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
22620002	6	6	74.36	99.3%	15.19	64.2%	YES	Evaluated	3b

Class C - Conventional 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
22620002	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	0.02	1.59	0.26	0.03	0	NO	Monitored	Full
22620002	6	pH	15 / 5	7.4	9.2	8.5	8.5	2	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)
168	tissue plug	2015	largemouth bass	4	38.8	0.3
Support Level	Not	A one meal/week mercury consumption advisory for largemouth bass exists on this lake. Based on IR Methodology, the Class HH (fish consumption) use was assessed as “not supported.”

Monitoring and Methods

Assessment Key Dates

6/22/2016

Fixed Monitoring Start Date

9/9/2020

Fixed Monitoring End Date

10/28/2002

TMDL Completed

9/24/2012

TMDL Completed

7/24/2015

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)