Silver Lake IA 06-LSR-1669

Dickinson County S28T100NR38W near Lake Park.

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
View assessment methodology in new window

Cycle: 2024
Release Status: Final
Overall IR: 1 - All designated uses are met.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:13:35 AM
Updated: 2/5/2024 1:13:30 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2022	Class A1	Turbidity: Secchi Disk Transparency	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “fully supported.” The Class BLW use was assessed (monitored) as “fully supported.” The Class C use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed (monitored) as "fully supported" based on fish tissue sampling data. Note: A TMDL for turbidity at Silver Lake was prepared by DNR and approved by EPA in 2009.

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	22300007	Silver Lake Max Depth
Iowa DNR	6	FT	See Below	1198	Silver Lake	Near Lake Park

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
22300007	6	12 / 4	8.2	9.1	8.6	1	4	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
22300007	6	Chlorophyll a TSI	32 / 5	8	84	56	NO	Mon	Full
22300007	6	Secchi TSI	32 / 5	45	73	62	NO	Mon	Full
22300007	6	Total Phosphorus TSI	32 / 5	53	92	76	NA	NA	NA
22300007	6	Inorganic suspended solids	28 / 5	0.7	38	2.8	NA	NA	NA

DNR's assessment methodology indicates that a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment. The Secchi depth TSI value for the 2022 assessment listing cycle was 65, 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 trigger of 63 (median TSI value for Secchi depth was 62), based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (5a) for Secchi depth is suggested for delisting for the 2024 assessment/listing cycle.

Class BLW - 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
22300007	6	Dissolved Oxygen	12 / 4	7.18	14.04	9.58	0	NA / NA	4	NO	Mon	Full
22300007	6	pH	12 / 4	8.2	9.1	8.6	1	NA / NA	4	NO	Mon	Full
22300007	6	Temperature	12 / 4	15.9	27.7	23	0	NA / NA	4	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
22300007	6	3	668.829443	100%	11.24972933	99%	NO	Evaluated	NA

Class BLW - 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
22300007	6	Ammonia	12 / 4	0.168	0.06	0.04	0 / 0	NO	Mon	Full

Class C - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22300007	6	Inorganic nitrogen (nitrate and nitrite)	31 / 5	0.01	4.32	1.39	0.97	0	NO	Mon	Full
22300007	6	pH	12 / 4	8.2	9.1	8.6	8.6	1	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)
1198	fillet	2014	channel catfish	5	45	0.03	0.1	0.06
1198	tissue plug	2019	northern pike	10	65.96	0.116
1198	tissue plug	2020	walleye	10	48.81	0.151
Support Level	Full

Monitoring and Methods

Assessment Key Dates

5/16/2018

Monitoring Start

9/11/2022

Monitoring End

7/28/2014

Fish Tissue Monitoring

10/24/2014

Fish Tissue Monitoring

9/9/2009

TMDL Completed

7/1/2019

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)