Ottumwa Lagoon IA 04-LDM-1014

Wapello County S25T72NR14W at Ottumwa.

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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 12/27/2021 2:37:21 PM
Updated: 1/28/2022 6:57:39 AM

Use Support

Class A1

Recreation - Primary contact

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

High

Cycle Added

1998

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

High

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Not Assessed

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as “not supported” due to aesthetically objectionable conditions caused by poor water transparency due to algal blooms and high levels of inorganic turbidity. All other designated uses were “not assessed.” Note: A TMDL for algae, turbidity, and chlordane at Ottumwa Lagoon was prepared by DNR and approved by EPA in 2005; thus, this waterbody was placed in Category 4a of Iowa's 2006 Integrated Report. Because all of the impairments are covered by this TMDL, this waterbody is placed in Category 4a of Iowa's current Integrated Report.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2019	22900001	Ottumwa Lagoon Max Depth

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
22900001	6	9 / 3	7.2	8.1	7.6	0	3	NO	Evaluated	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
22900001	6	Chlorophyll a TSI	9 / 3	44	76	61	NO	Monitored	Full
22900001	6	Secchi TSI	9 / 3	70	89	81	YES	Monitored	Not
22900001	6	Total Phosphorus TSI	9 / 3	75	86	81	NA	NA	NA
22900001	6	Inorganic suspended solids	9 / 3	8	115	16	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, the Class A1 use of Ottumwa Lagoon remains "not supported" 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, Ottumwa Lagoon will remain listed as "not supported" 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
22900001	6	Ammonia	9 / 3	0.009	0.076	0.03	NA	0 / 0	3	NO	Evaluated	Full
22900001	6	Dissolved Oxygen	9 / 3	5.1	8.9	7	0	NA / NA	3	NO	Evaluated	Full
22900001	6	pH	9 / 3	7.2	8.1	7.6	0	NA / NA	3	NO	Evaluated	Full
22900001	6	Temperature	9 / 3	16	29.1	24	0	NA / NA	3	NO	Evaluated	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
22900001	6	6	1.78	21.4%	0.20	1.4%	NO	Evaluated	NA

Class HH: No Data

Monitoring and Methods

Assessment Key Dates

8/28/2019

Non-fixed Monitoring End Date

5/25/2016

Non-fixed Monitoring Start Date

12/28/2005

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

222

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

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)