Silver Lake IA 04-UDM-1229

Palo Alto County S20T95NR34W 2 mi W of Ayrshire.

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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 8/14/2020 1:59:04 PM
Updated: 10/19/2020 10:15:16 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Agriculture

Source Confidence

High

Cycle Added

2002

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Turbidity

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Agriculture

Source Confidence

High

Cycle Added

2002

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2018

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2018

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use is assessed (monitored) as “not supported” due to poor water transparency caused by inorganic suspended solids, algae blooms that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions and due to frequent violations of the state criterion for pH. The Class BLW use is assessed (monitored) as "not supported" due to violations of the Class B(LW) criterion for pH. All other designated uses are “not assessed.” Note: A TMDL for algae and turbidity at Silver Lake was prepared by DNR and approved by EPA in 2005. Thus, these impairments are moved from IR Category 5a (impaired; TMDL required) to Category 4a (impaired; TMDL approved). Because not all the impairments identified for this lake are covered by this TMDL (pH), this lake remains in IR Category 5a.

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2014-2018	22740003	Silver Lake (Palo Alto County)

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22740003	6	15 / 5	9.55	8.73	8.8	5	33%	YES	Monitored	Not

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
22740003	6	Chlorophyll a TSI	15 / 5	41	83	70	YES	Monitored	Not
22740003	6	Secchi TSI	15 / 5	60	83	77	YES	Monitored	Not
22740003	6	Total Phosphorus TSI	15 / 5	61	92	81	NA	NA	NA
22740003	6	Inorganic suspended solids	15 / 5	4	128	13	NA	NA	NA

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
22740003	6	Ammonia	15 / 5	0.71	0.12	0.07	0 / 0	0% / 0%	NO	Monitored	Full
22740003	6	Dissolved oxygen	15 / 5	15.9	10.6	10.2	NA / 0	NA / 0%	NO	Monitored	Full
22740003	6	pH	15 / 5	9.55	8.73	8.8	5 / NA	33% / NA	YES	Monitored	Not
22740003	6	Temperature	15 / 5	27.3	22.9	22.6	0 / 0	0% / 0%	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 Wet Mass = 75th Percentile	Assessment Type	Support Level
22740003	6	10	250.487	99.4 %	17.636	74.2 %	NO	Evaluated	NA

Class BLW - Fish Kill:

The Class BLW uses that were assessed (evaluated) as "partially supporting" due to a fish kill in 2004 has been removed based on the assessment methodology. The 3b impairment is switched to 3a "not assessed" based on the age of the non-pollutant caused fish kill.

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

6/2/2014

Fixed Monitoring Start Date

9/5/2018

Fixed Monitoring End Date

4/3/2006

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

222

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)