East Lake (Osceola) IA 04-LDM-1065

Clarke County S16T72NR25W 0.5 mi E of Osceola.

Assessment Cycle

2022

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 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.

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

Created: 12/28/2021 8:58:05 AM
Updated: 2/4/2022 7:17:04 AM

Assessment conducted in accordance with Iowa's 2022 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

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

Aquatic Life

Lakes and wetlands

WINOFI

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

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

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

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 poor water transparency. The Class BLW use was assessed (evaluated) as "WINOFI" due to excessive nutrient loading to the water column and impacts from organic enrichment. All other designated uses were “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 were 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, this lake remains in IR Category 4a.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2020	22200001	East Lake Osceola

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
22200001	6	15 / 5	6.7	9.1	8.2	1	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
22200001	6	Chlorophyll a TSI	15 / 5	36	88	59	NO	Monitored	Full
22200001	6	Secchi TSI	15 / 5	47	83	67	YES	Monitored	Not
22200001	6	Total Phosphorus TSI	15 / 5	63	100	87	NA	NA	NA
22200001	6	Inorganic suspended solids	15 / 5	0.3	8	3.1	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 chlorophyll a TSI value for the 2002 assessment listing cycle was 67, 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 chlorophyll a was 60), and because the TSI value for the current listing cycle is 59, based on DNR's methodology, these values suggest "full support" of the Class A1 use protecting against aesthetically objectionable conditions and the impairment (4a) for chlorophyll a 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
22200001	6	Ammonia	15 / 5	0.0003	0.447	0.1	NA	0 / 0	4	NO	Monitored	Full
22200001	6	Dissolved Oxygen	14 / 5	3.6	11.3	6.9	3	NA / NA	4	NO	Monitored	Full
22200001	6	pH	15 / 5	6.7	9.1	8.2	1	NA / NA	4	NO	Monitored	Full
22200001	6	Temperature	15 / 5	17.1	28.8	24.1	0	NA / NA	4	NO	Monitored	Full

Note: The Class BLW use was assessed (evaluated) as “WINOFI” 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 Concentration = 75th Percentile	Assessment Type	Support Level
22200001	6	6	19.54	89.0%	3.82	3.5%	NO	Evaluated	NA

Class HH: No Data

Monitoring and Methods

Assessment Key Dates

5/23/2016

Non-fixed Monitoring Start Date

9/8/2020

Non-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)