Silver Lake IA 06-LSR-1669

Dickinson County S28T100NR38W near Lake Park.

This is a DRAFT assessment

Draft assessments may change without notice

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 2022 - 2024
Stream/River Water Quality Data	CY 2022 - 2024
Lake Water Quality Data	CY 2020 - 2024
Biological Sampling Data	CY 2020 - 2024*
Fish Kill Data	CY 2020 - 2024
Fish Tissue Sampling Data	CY 2020 - 2024
Continuous Dissolved Oxygen Sampling Data	CY 2020 - 2024
*Biological sites sampled in both 2019 and 2023 were also assessed.

Open Segment Map
View 2026 assessment summary page

Cycle: 2026
Current Phase: Public Comment
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 10/27/2025 3:10:32 PM
Updated: 1/12/2026 11:57:52 AM

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

Moderate

Status

New

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2026

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier IV

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

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 aesthetically objectionable conditions caused by algae blooms. The Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. 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 2020-2024	22300007	Silver Lake Max Depth
Iowa DNR	6	FT	See Below	1198	Silver Lake

Class A - 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	8.7	1	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
22300007	6	Chlorophyll a TSI	20 / 5	26	89	66	YES	MONITORED	NOT
22300007	6	Secchi TSI	20 / 5	46	80	61	NO	MONITORED	FULL
22300007	6	Total Phosphorus TSI	20 / 5	54	96	77	NA	NA	NA
22300007	6	Fixed suspended solids	18 / 5	0.7	20	2.5	NA	NA	NA

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	7.8	14	9.8	0	NA / NA	4	NO	MONITORED	FULL
22300007	6	pH	12 / 4	8.2	9.1	8.7	1	NA / NA	4	NO	MONITORED	FULL
22300007	6	Temperature	12 / 4	18.4	27.3	23.5	0	NA / NA	4	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
22300007	6	4	668.829443	99.83%	68.480649	99.34%	YES	EVALUATED	WINOFI

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	0.361	0.13	0.09	0 / 1	NO	MONITORED	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)	19 / 5	0.01	4.26	0.95	0.27	0	NO	MONITORED	FULL
22300007	6	pH	12 / 4	8.2	9.1	8.7	8.7	1	NO	MONITORED	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	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

5/28/2020

Monitoring Start

9/10/2024

Monitoring End

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)