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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 7/30/2020 10:27:37 AM
Updated: 10/14/2020 10:35:45 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially 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

Algal Growth: Chlorophyll a

Support Level

Partially Supported

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Agriculture

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

Not Assessed

Class HH

Human Health -

Partially Supported

Fish Consumption Advisory: Mercury

Support Level

Partially 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

General Use

General Use water -

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2014	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 uses are assessed (monitored) as “not supported” due to levels of indicator bacteria (IR 5a) and due to aesthetically objectionable conditions caused by algae blooms (IR 4a) that exceed Iowa’s water quality standards. The Class BLW uses are assessed (monitored) as “fully supported.” The Class C uses remain “not assessed” (IR 3a) due to a lack of enough information on which to base an assessment. Class HH uses remain assessed (monitored) as "partially supported" (IR 5a) due to the issuance of a fish consumption advisory at this lake. 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

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2018	21620001	Lake Keomah Beach (Lake Keomah State Park)	Beach
Iowa DNR	6	WQ	CY 2014-2018	22620002	Lake Keomah	Lake Deep Point
Iowa DNR		FT	See Below	168	Lake Keomah

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2016 Geometric Mean	2017 Geometric Mean	2018 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
21620001	6	38 / 3	85.66	43.01	49.31	No	9	24%	YES	Monitored	Partial

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22620002	6	15 / 5	9	8.4	8.5	0	0%	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	63	NO	Monitored	Full
22620002	6	Secchi TSI	15 / 5	44	78	60	NO	Monitored	Full
22620002	6	Total Phosphorus TSI	15 / 5	50	80	64	NA	NA	NA
22620002	6	Inorganic suspended solids	15 / 5	0.3	18	2.4	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Lake Darling was listed as partially supporting its Class A1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 4a). Therefore, Lake Darling will remain listed as "not supported" for the 2020 assessment/listing cycle.

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
22620002	6	Ammonia	15 / 5	0.33745	0.09	0.03	0 / 0	0% / 0%	NO	Monitored	Full
22620002	6	Dissolved oxygen	15 / 5	12	8.5	8.2	NA / 0	NA / 0%	NO	Monitored	Full
22620002	6	pH	15 / 5	9	8.4	8.5	0 / NA	0% / NA	NO	Monitored	Full
22620002	6	Temperature	15 / 5	28.5	24.3	24.5	0 / 0	0% / 0%	NO	Monitored	Full

Lake Keomah was assessed as "partially supported" for the 2014 assessment/listing cycle. Based on DNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on Dissolved Oxygen violations. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2018 or current 2020 assessment listing cycle. Therefore, the impairment for Dissolved Oxygen is suggested for delisting for the 2020 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 Wet Mass = 75th Percentile	Assessment Type	Support Level
22620002	6	11	172.483	99.8 %	34.291	78.7 %	YES	Evaluated	3b

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22620002	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	0.9	0.15	0.03	0	0%	NO	Monitored	Full

The Class C uses are not assessed due to the lack of data sufficient for developing a valid assessment of support of the Class C uses.

Class HH - Fish Tissue Sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation?

PCBs result

PCBs violation?

Hg result

Hg violation?

Assessment Type

Support Level

168

7/24/15

largemouth bass

plug

0.300

Monitored

Full

168

7/27/10

largemouth bass

fillet

0.432

Yes

Evaluated

Partial

168

10/26/09

largemouth bass

fillet

0.464

Yes

Evaluated

Partial

168

10/26/09

channel catfish

fillet

<0.03

<0.09

0.027

Evaluated

Full

Monitoring and Methods

Assessment Key Dates

7/16/2014

Fixed Monitoring Start Date

9/9/2018

Fixed Monitoring End Date

10/26/2009

Fish Tissue Monitoring

7/27/2010

Fish Tissue Monitoring

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)