2020 Final assessment for East Lake (Osceola)

East Lake (Osceola) IA 04-LDM-1065

Clarke County S16T72NR25W 0.5 mi E of Osceola.

Assessment Cycle

2020

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 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.

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

Created: 8/12/2020 2:20:22 PM
Updated: 10/14/2020 11:35:06 AM

Assessment conducted in accordance with Iowa's 2020 IR methodology

Use Support

Class A1

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2002

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Turbidity

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

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

Class BLW

WINOFI

Nutrients

Support Level

Water in Need of Further Investigation (WINOFI)

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2002

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Sedimentation/Siltation

Support Level

Water in Need of Further Investigation (WINOFI)

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Low

Cycle Added

2002

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Class HH

Not Assessed

General Use

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2016	Class A1	pH	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)
2016	Class BLW	pH	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 uses of East Lake are assessed (monitored) as "not supported" due to poor water transparency and aesthetically objectionable conditions caused by algae blooms. The Class BLW uses are assessed (evaluated) as "not supported" due to excessive nutrient loading to the water column, and impacts from organic enrichment. All other designated uses are “not assessed.” NOTE: A TMDL for algae and turbidity for East Lake was completed by DNR and approved by EPA in 2008. Thus, these impairments are moved from IR Category 5a (impaired; TMDL required) to Category 4a (impaired; TMDL approved). Because all the impairments identified for this lake are covered by this TMDL (pH), this lake is placed IR Category 4a.

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 2014-2018	22200001	East Lake Osceola

Class A1 - Indicator Bacteria: No Data

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
22200001	6	15 / 5	9.15	8.38	8.5	1	7%	NO	Monitored	Full

East Lake (Osceola) was assessed as "not supported" for the 2016 assessment/listing cycle due to frequent violations of the state Class A1 criterion for pH. 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 pH 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 pH is suggested for delisting for the 2020 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
22200001	6	Chlorophyll a TSI	15 / 5	36	75	60	NO	Monitored	Full
22200001	6	Secchi TSI	15 / 5	47	77	67	YES	Monitored	Not
22200001	6	Total Phosphorus TSI	15 / 5	75	95	86	NA	NA	NA
22200001	6	Inorganic suspended solids	15 / 5	0.3	30.8	5	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, East Lake (Osceola) 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 5). Therefore, East Lake (Osceola) 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
22200001	6	Ammonia	15 / 5	0.447	0.09	0.03	0 / 0	0% / 0%	NO	Monitored	Full
22200001	6	Dissolved oxygen	15 / 5	15.66	8.42	7.6	NA / 1	NA / 7%	NO	Monitored	Full
22200001	6	pH	15 / 5	9.15	8.38	8.5	1 / NA	7% / NA	NO	Monitored	Full
22200001	6	Temperature	15 / 5	28.8	23.4	23.3	0 / 0	0% / 0%	NO	Monitored	Full

Note:The Class BLW uses are assessed (evaluated) as “partially supported” due to algae blooms and poor water quality that put the lake at risk for a fish kill based on information from the DNR Fisheries bureau.

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
22200001	6	11	84.452	89 %	15.923	44.6 %	NO	Evaluated	NA

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/27/2014	Fixed Monitoring Start Date
8/22/2018	Fixed Monitoring End Date
5/14/2008	TMDL Completed

Methods

120	Surveys of fish and game biologists/other professionals
222	Non-fixed-station monitoring (conventional during key seasons and flows)
340	Primary producer surveys (phytoplankton/periphyton/macrophyton)

Water Quality Assessments

Impaired Waters List

East Lake (Osceola) IA 04-LDM-1065

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods