Lake Manawa IA 06-WEM-1711

Pottawattamie County S13T74NR44W S edge Council Bluffs

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
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Cycle: 2024
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 11/1/2023 8:13:38 AM
Updated: 2/5/2024 1:21:34 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier IV

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2024

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Beach monitoring: Iowa DNR WQMA

TMDL Priority

Tier II

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2004	Class A1	Algal Growth: Chlorophyll a	Ambient monitoring: Iowa DNR-lakes	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to high levels of indicator bacteria and due to the occurrence of aesthetically objectionable conditions caused by poor water transparency related to non-algal turbidity. The Class BLW 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.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2020-2022	21780001	Lake Manawa Beach
Iowa DNR	6	WQ	CY 2018-2022	22780003	Lake Manawa
Iowa DNR	6	FT	See Below	1066	Lake Manawa	S of Council Bluffs

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2020/ 2021/2022)

2020 Geometric Mean

2021 Geometric Mean

2022 Geometric Mean

Violates Annual Geometric Mean?

# 2020 SSM violations / SSM Violations needed for impairment

# 2021 SSM violations / SSM Violations needed for impairment

# 2022 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

21780001

16/13/15

3 / 4

4 / 4

YES

Mon

Not

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
22780003	6	12 / 4	8	8.93	8.42	0	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
22780003	6	Chlorophyll a TSI	12 / 4	44	77	62	NO	Mon	Full
22780003	6	Secchi TSI	12 / 4	64	83	76	YES	Mon	Not
22780003	6	Total Phosphorus TSI	12 / 4	55	80	72	NA	NA	NA
22780003	6	Inorganic suspended solids	12 / 4	6	24	12	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
22780003	6	Dissolved Oxygen	12 / 4	4.8	10.2	8.1	1	NA / NA	4	NO	Mon	Full
22780003	6	pH	12 / 4	8	8.93	8.42	0	NA / NA	4	NO	Mon	Full
22780003	6	Temperature	12 / 4	21.9	29.6	25.7	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
22780003	6	5	51.81595231	86%	5.279796826	50%	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
22780003	6	Ammonia	12 / 4	0.063	0.02	0.02	0 / 0	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)
1066	fillet	2015	channel catfish	5	46.5	0.02	0.02	0.06
1066	tissue plug	2020	common carp	20	54.6	0.015
1066	tissue plug	2021	hybrid striped bass	6		0.020
1066	tissue plug	2020	hybrid striped bass	4	46.0	0.031
1066	tissue plug	2020	yellow bass	10	17.1	0.021
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/4/2018

Monitoring Start

9/18/2022

Monitoring End

7/29/2015

Fish Tissue Monitoring

8/26/2015

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

5/10/2021

Fish Tissue Monitoring

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring