Clear Lake IA 02-WIN-841

Cerro Gordo County S13T96NR22W at Clear Lake.

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.

Open Segment Map
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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 7/29/2020 12:44:44 PM
Updated: 10/14/2020 10:20:53 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

High

Cycle Added

2004

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Beach monitoring: Iowa DNR city/county

TMDL Priority

Tier II

Turbidity

Support Level

Partially Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Moderate

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Algal Growth: Cyanobacteria

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class C

Drinking Water -

Not Assessed

Class HH

Human Health -

Fully Supported

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 “partially supported” due to violations of the state water quality criteria for indicator bacteria. In addition, the ISU lake surveys suggest “partial support” of the Class A1 uses due to poor water transparency primarily due to high levels of inorganic suspended solids. The Class BLW use remains assessed (evaluated) as “partially supported” due to cyanobacteria blooms. The Class C use is “not assessed” due to a lack of enough information upon which to base an assessment. Class HH use remains assessed (evaluated) as “fully supported” based on fish tissue sampling. All other designated uses are “not assessed”. Note: A TMDL for turbidity and algae at Clear Lake was prepared by DNR and approved by EPA in 2005. Because the Section 303(d) impairments due to indicator bacteria were not addressed in the TMDL, this waterbody will remain in Category 5a (impaired; TMDL required) of Iowa's current Integrated Report.

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 2016-2018	21170001	Clear Lake State Park Beach (Clear Lake State Park)
Iowa DNR	6	WQ	CY 2016-2018	21170002	McIntosh Beach (McIntosh Woods State Park)
Iowa DNR	6	WQ	CY 2014-2018	22170001	Clear Lake
Iowa DNR		FT	See Below	122	Clear Lake

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2016 Geometric Mean	2017 Geometric Mean	2018 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
21170001	6	45 / 3	54.81	15.69	36.32	No	5	11%	NO	Monitored	Full
21170002	6	45 / 3	544.96	145.01	184.57	Yes	23	51%	YES	Monitored	Partial

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
22170001	6	15 / 5	8.68	8.35	8.3	0	0%	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
22170001	6	Chlorophyll a TSI	15 / 5	36	68	57	NO	Monitored	Full
22170001	6	Secchi TSI	15 / 5	54	73	65	YES	Monitored	Not
22170001	6	Total Phosphorus TSI	15 / 5	51	68	61	NA	NA	NA
22170001	6	Inorganic suspended solids	15 / 5	1	11.5	3	NA	NA	NA

DNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment. The chlorophyll a TSI value for the 2002 assessment listing cycle was 73, 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 2018 assessment/listing cycle was less than the trigger of 65 (2018 listing for chlorophyll a was 60), and because the TSI value for the current listing cycle is also 57, based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (4a) for chlorophyll a is suggested for removal for the 2020 assessment/listing cycle.

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
22170001	6	Ammonia	15 / 5	0.211	0.03	0.01	0 / 0	0% / 0%	NO	Monitored	Full
22170001	6	Dissolved oxygen	15 / 5	11.5	8.3	8.1	NA / 0	NA / 0%	NO	Monitored	Full
22170001	6	pH	15 / 5	8.68	8.35	8.3	0 / NA	0% / NA	NO	Monitored	Full
22170001	6	Temperature	15 / 5	26.3	22.9	22.8	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
22170001	6	11	586.271	99.9 %	171.977	96.4 %	YES	Evaluated	3b

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22170001	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	0.15735	0.0355	0.03	0	0%	NO	Monitored	Full

The Class C uses are not assessed due to the lack of data sufficient for developing a valid assessment of support of the Class C uses.

Class HH – Fish Tissue Sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation?

PCBs result

PCBs violation?

Hg result

Hg violation?

Assessment Type

Support Level

122

9/7/12

channel catfish

fillet

<0.03

<0.09

0.0306

Evaluated

Full

122

9/24/12

walleye

plug

0.075

Evaluated

Full

Note:A dredging project was completed in 2009, which will likely reduce the internal resuspension of sediment and phosphorus in the lake for future assessments. Additionally, a population of zebra mussels has developed in the lake. Sediment, phosphorus, and algae levels have all declined slightly since the 2010 assessment and listing cycle.

Monitoring and Methods

Assessment Key Dates

6/11/2014

Fixed Monitoring Start Date

9/19/2018

Fixed Monitoring End Date

9/24/2012

Fish Tissue Monitoring

9/7/2012

Fish Tissue Monitoring

3/10/2005

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

222

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

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring