Rathbun Reservoir - Main Basin IA 05-CHA-1309

Appanoose County approx 6 miles N of Centerville.

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Open Segment Map
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Cycle: 2024
Release Status: Final
Overall IR: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:13:43 AM
Updated: 2/5/2024 2:29:27 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

Class HH

Human Health -

WINOFI

Metals: Mercury

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

New

Source

Atmospheric Deposition

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Potential Impairment

Data Source

Fish contaminant monitoring: Iowa DNR

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "fully supported.” The Class BWW1 use was assessed as "fully supported" based water quality monitoring. The Class HH (fish consumption) use was assessed (evaluated) as “WINOFI” based on fish tissue sampling data. Note: A TMDL for turbidity at four segments of Rathbun Lake was prepared by DNR and approved by EPA in 2019.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2022	22040001	Rathbun Lake
USACE	12	WQ	CY 2018-2022	99990023	Rathbun Reservoir
PWS	27	WQ	CY 2018-2022	99990179	Caisson - Rathbun Lake Dedication	Rathbun Regional Water Association
Iowa DNR	6	FT	See Below	1053	Rathbun Reservoir

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
22040001	6	12 / 4	7.5	8.6	7.8	0	4	NO	Mon	Full
99990023	12	10 / 2	7.67	8.62	8.14	0	3	NO	Mon	Full
99990179	27	1825 / 5	7.2	8.5	7.7	0	200	NO	Mon	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
22040001	6	Chlorophyll a TSI	12 / 4	26	60	44	NO	Mon	Full
99990023	12	Chlorophyll a TSI	27 / 5	0	74	49	NO	Mon	Full
22040001	6	Secchi TSI	12 / 4	44	76	62	NO	Mon	Full
99990023	12	Secchi TSI	27 / 5	54	73	63	NO	Mon	Full
22040001	6	Total Phosphorus TSI	12 / 4	54	78	58	NA	NA	NA
99990023	12	Total Phosphorus TSI	28 / 5	53	80	70	NA	NA	NA
22040001	6	Inorganic suspended solids	12 / 4	0.6	6	2	NA	NA	NA

DNR's assessment methodology indicates that a TSI value less than or equal to 63 is necessary to suggest de-listing of an impairment. The Secchi depth TSI value for the 2012 assessment listing cycle was 70, 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 2024 assessment/listing cycle is less than or equal to the delisting threshold of 63 (median TSI value for Secchi depth was 62,63), based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (4a) for Secchi depth is suggested for removal for the 2024 assessment/listing cycle.

Class BWW1 - Binomial 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
22040001	6	Dissolved Oxygen	12 / 4	3.9	8	6.2	3	NA / NA	4	NO	Mon	Full
99990023	12	Dissolved Oxygen	28 / 5	4.98	11.35	8.29	1	NA / NA	6	NO	Mon	Full
22040001	6	pH	12 / 4	7.5	8.6	7.8	0	NA / NA	4	NO	Mon	Full
99990023	12	pH	10 / 2	7.67	8.62	8.14	0	NA / NA	3	NO	Mon	Full
99990179	27	pH	1825 / 5	7.2	8.5	7.7	0	NA / NA	200	NO	Mon	Full
22040001	6	Temperature	12 / 4	17.3	27	23.5	0	NA / NA	4	NO	Mon	Full
99990023	12	Temperature	28 / 5	7.9	28.3	21.7	0	NA / NA	6	NO	Mon	Full
99990179	27	Temperature	1823 / 5	5	25.25	14.66	0	NA / NA	200	NO	Mon	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
22040001	6	3	1.74509012	57%	1.48236927	8%	NO	Evaluated	NA

Class BWW1 - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
22040001	6	Ammonia	12 / 4	0.093	0.04	0.03	0 / 0	NO	Mon	Full
99990023	12	Ammonia	10 / 2	0.16	0.07	0.07	0 / 0	NO	Mon	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)
1053	tissue plug	2021	flathead catfish	14		0.357
1053	tissue plug	2020	flathead catfish	6	49.0	0.242
1053	tissue plug	2019	flathead catfish	8	45.0	0.174
1053	tissue plug	2019	largemouth bass	10	38.8	0.102
1053	tissue plug	2017	largemouth bass	3	42.1	0.223
1053	tissue plug	2019	walleye	20	47.3	0.062
Support Level	WINOFI

Monitoring and Methods

Assessment Key Dates

1/1/2018

Monitoring Start

12/31/2022

Monitoring End

9/17/2017

Fish Tissue Monitoring

7/1/2019

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

7/7/2021

Fish Tissue Monitoring

6/14/2019

TMDL Completed

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring