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 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: Eutrophic
Trend: Stable
Created: 1/5/2022 1:52:08 PM
Updated: 1/27/2022 12:41:37 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Moderate

Cycle Added

2012

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Corps of Engineers/Iowa DNR/ISU

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "not supported” due to high levels of non-algal turbidity that create aesthetically objectionable conditions. The Class BWW1 use was assessed as "fully supported" based water quality monitoring. The Class HH (fish consumption) use was assessed (monitored) as “fully supported” 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. Because all Section 303(d) impairments identified for the current assessment/listing cycle are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

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	22040001	Rathbun Lake
USACE	12	WQ	CY 2016-2020	99990023	Rathbun Reservoir
Iowa DNR	6	FT	See Below	53	Rathbun Reservoir

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

22040001

3/3/0

0 / NA

Evaluated

Full

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	8.5	7.8	0	4	NO	Monitored	Full
99990023	12	5 / 2	7.84	8.65	8.15	0	2	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
22040001	6	Chlorophyll a TSI	12 / 4	26	56	34	NO	Monitored	Full
99990023	12	Chlorophyll a TSI	27 / 5	34	74	50	NO	Monitored	Full
22040001	6	Secchi TSI	12 / 4	44	77	66	YES	Monitored	Not
99990023	12	Secchi TSI	26 / 5	54	82	70	YES	Monitored	Not
22040001	6	Total Phosphorus TSI	12 / 4	54	78	62	NA	NA	NA
99990023	12	Total Phosphorus TSI	28 / 5	53	80	68	NA	NA	NA
22040001	6	Inorganic suspended solids	12 / 4	0.3	15.6	3.2	NA	NA	NA

Class BWW1 - 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
22040001	6	Ammonia	12 / 4	0.0003	0.103	0.03	NA	0 / 0	4	NO	Monitored	Full
99990023	12	Ammonia	5 / 2	0.01	0.05	0.03	NA	0 / 0	2	NO	Evaluated	Full
22040001	6	Dissolved Oxygen	12 / 4	3.9	8.6	6.5	3	NA / NA	4	NO	Monitored	Full
99990023	12	Dissolved Oxygen	26 / 5	4.98	11.14	8.19	1	NA / NA	6	NO	Monitored	Full
22040001	6	pH	12 / 4	7.5	8.5	7.8	0	NA / NA	4	NO	Monitored	Full
99990023	12	pH	5 / 2	7.84	8.65	8.15	0	NA / NA	2	NO	Evaluated	Full
22040001	6	Temperature	12 / 4	15.1	27	22.4	0	NA / NA	4	NO	Monitored	Full
99990023	12	Temperature	27 / 5	9	30	22	0	NA / NA	6	NO	Monitored	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	6	8.33	86.8%	0.92	18.6%	NO	Evaluated	NA

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)
53	tissue plug	2020	flathead catfish	6	49.0	0.242
53	tissue plug	2019	flathead catfish	8	45.0	0.174
53	tissue plug	2019	largemouth bass	10	38.8	0.102
53	tissue plug	2017	largemouth bass	3	42.1	0.223
53	tissue plug	2019	walleye	20	47.3	0.062
Support Level	Full

Monitoring and Methods

Assessment Key Dates

4/14/2016

Non-fixed Monitoring Start Date

9/17/2020

Non-fixed Monitoring End Date

9/17/2017

Fish Tissue Monitoring

7/1/2019

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

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

240

Non-fixed station physical/chemical (conventional + toxicants)

260

Fish tissue analysis

330

Fish surveys

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring