Gustafson Lake IA 06-LSR-1625

Buena Vista County S18T93NR36W 1 mi S of Sioux Rapids.

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: Unknown
Trend: Unknown
Created: 1/4/2022 8:16:41 AM
Updated: 2/2/2022 2:47:29 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Slight

Status

Continuing

Source

Hydromodification: Erosion and Sedimentation

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Single-sample maximum criterion exceeded in significantly > 10% of samples

Data Source

Beach monitoring: Iowa DNR city/county

TMDL Priority

Tier II

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

N/A

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

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 (monitored) as "not supported" due to violations of the state's criteria for indicator bacteria based on historical results of the county beach monitoring program at Gabrielson Park beach and due to poor water transparency caused by non-algal turbidity. 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 2018-2020	22110002	Gustafson Lake
Iowa DNR	6	WQ	CY 2014-2016	21110001	Gabrielson Park Beach

Class A1 - Indicator Bacteria: Historical 2018 Assessment

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	2015 Geometric Mean	2016 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
21110001	6	26 / 2	101	NA	19	No	2	8%	NO	Monitored	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Gustafson Lake will remain listed for this assessment cycle as "not supported" its Class A1 use due to indicator bacteria.

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
22110002	6	9 / 3	7.9	8.3	8.1	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
22110002	6	Chlorophyll a TSI	9 / 3	26	74	61	NO	Monitored	Full
22110002	6	Secchi TSI	9 / 3	60	73	67	YES	Monitored	Not
22110002	6	Total Phosphorus TSI	9 / 3	59	75	65	NA	NA	NA
22110002	6	Inorganic suspended solids	9 / 3	0.6	12	1.6	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
22110002	6	Ammonia	9 / 3	0.0068	0.5785	0.1	NA	0 / 0	3	NO	Evaluated	Full
22110002	6	Dissolved Oxygen	9 / 3	7.2	14.7	10.7	0	NA / NA	3	NO	Evaluated	Full
22110002	6	pH	9 / 3	7.9	8.3	8.1	0	NA / NA	3	NO	Evaluated	Full
22110002	6	Temperature	9 / 3	17.4	25.2	22.4	0	NA / NA	3	NO	Evaluated	Full

Class HH: No Data

Monitoring and Methods

Assessment Key Dates

9/14/2020

Fixed Monitoring End Date

6/4/2018

Fixed Monitoring Start Date

Methods

220

Non-fixed station physical/chemical monitoring (conventional pollutant only)

420

Indicator bacteria monitoring