Rodgers Park Lake IA 02-CED-526

Benton County S1T86NR11W 3.5 mi NW of Vinton.

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: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/17/2021 10:52:43 AM
Updated: 2/3/2022 1:08:43 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Agriculture

Source Confidence

Low

Cycle Added

2022

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2018	Class BLW	Organic Enrichment: Low Dissolved Oxygen	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed as "not supported" due to the presence of aesthetically objectionable conditions caused by algal blooms. The Class BLW use was assessed as “fully supported.” All other designated uses were “not assessed.”

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	22060002	Rodgers Lake

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
22060002	6	15 / 5	7.5	8.9	8.2	0	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
22060002	6	Chlorophyll a TSI	15 / 5	36	83	66	YES	Monitored	NOT
22060002	6	Secchi TSI	14 / 5	42	77	66	YES	Monitored	NOT
22060002	6	Total Phosphorus TSI	15 / 5	53	92	73	NA	NA	NA
22060002	6	Fixed suspended solids	15 / 5	0.4	12	3	NA	NA	NA

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
22060002	6	Ammonia	15 / 5	0.0003	0.412	0.12	NA	0 / 0	4	NO	Monitored	FULL
22060002	6	Dissolved Oxygen	15 / 5	3.6	19.2	10	1	NA / NA	4	NO	Monitored	FULL
22060002	6	pH	15 / 5	7.5	8.9	8.2	0	NA / NA	4	NO	Monitored	FULL
22060002	6	Temperature	15 / 5	18.5	27.6	23.6	0	NA / NA	4	NO	Monitored	FULL

Rodgers Lake was assessed as "not supported" for the 2018 assessment/listing cycle based on Dissolved Oxygen. 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 Dissolved Oxygen violations. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2020 or current 2022 assessment listing cycle. Therefore, the impairment for Dissolved Oxygen is suggested for delisting for the 2022 assessment/listing cycle.

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
22060002	6	6	219.39	87.8%	1.01	3.3%	NO	Evaluated	NA

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

6/7/2016

Fixed Monitoring Start Date

9/15/2020

Fixed Monitoring End Date

Methods

222

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)