North Twin Lake IA 04-RAC-1167

Calhoun County S1T88NR33W 4 mi N of Rockwell City.

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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Unknown
Created: 8/14/2020 9:46:47 AM
Updated: 10/14/2020 11:53:53 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

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2010

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Algal Growth: Noxious Aquatic Plants - Algae

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2010

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

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2010

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

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2012	Class A1	Bacteria: Indicator Bacteria- E. coli	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use is assessed (monitored) as “not supported” due to high levels chlorophyll a (algae) and non-algal turbidity that creates aesthetically objectionable conditions. The Class BLW use remains assessed (evaluated) as “partially supported” due to cyanobacteria blooms. Class HH use remains assessed as “fully supported” based on fish tissue sampling. Note: A TMDL for nutrients, algae, and turbidity at North Twin Lake was prepared by DNR and approved by EPA in 2004. Because the primary Section 303(d) impairment identified for the current assessment/listing cycle (algae and turbidity) is addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

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	21130001	North Twin Lake West Beach
Iowa DNR	6	WQ	CY 2016-2018	21130002	North Twin Lake East Beach
Iowa DNR	6	WQ	CY 2016-2016	21130003	Treman Park Beach
Iowa DNR	6	WQ	CY 2014-2018	22130001	North Twin Lake (maximum water depth)
Iowa DNR		FT	See Below	149	North Twin 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
21130001	6	41 / 3	13	19.09	24.42	No	0	0%	NO	Monitored	Full
21130002	6	33 / 3	9.13	13.56	17.08	No	0	0%	NO	Monitored	Full
21130003	6	14 / 1	65.19	NA	NA	No	3	21%	NO	Monitored	Full

North Twin Lake was assessed as "partially supported" for the 2012 assessment/listing cycle. Based on DNR’s assessment methodology 2 consecutive assessment/listing cycles without violations of the geometric mean criterion and without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on bacteria violations. There were no violations of the geometric mean criterion and there were less than 10% of the samples exceeding the single-sample maximum criterion for the 2018or current 2020assessment listing cycle. Therefore, the impairment for indicator bacteria is suggested for delisting for the 2020 assessment/listing cycle.

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
22130001	6	15 / 5	8.92	8.37	8.4	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
22130001	6	Chlorophyll a TSI	15 / 5	36	78	72	YES	Monitored	Not
22130001	6	Secchi TSI	15 / 5	70	83	73	YES	Monitored	Not
22130001	6	Total Phosphorus TSI	15 / 5	62	73	67	NA	NA	NA
22130001	6	Inorganic suspended solids	15 / 5	2	16	7	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
22130001	6	Ammonia	15 / 5	0.627	0.14	0.12	0 / 0	0% / 0%	NO	Monitored	Full
22130001	6	Dissolved oxygen	15 / 5	24	10	9	NA / 0	NA / 0%	NO	Monitored	Full
22130001	6	pH	15 / 5	8.92	8.37	8.4	0 / NA	0% / NA	NO	Monitored	Full
22130001	6	Temperature	15 / 5	26.6	21.8	23.6	0 / 0	0% / 0%	NO	Monitored	Full

Class BLW - Fish Kill:

The Class BLW uses that were assessed (evaluated) as "partially supporting" due to a fish kill in 2004 have 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 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
22130001	6	11	540.295	99.3 %	90.966	90.3 %	YES	Evaluated	3b

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

149

9/14/15

channel catfish

fillet

<0.02

<0.06

0.04

Monitored

Full

149

9/18/15

walleye

plug

0.050

Monitored

Full

Monitoring and Methods

Assessment Key Dates

5/19/2014

Fixed Monitoring Start Date

8/14/2018

Fixed Monitoring End Date

9/14/2015

Fish Tissue Monitoring

12/14/2004

TMDL Completed

9/18/2015

Fish Tissue Monitoring

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)

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring