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 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: Hypereutrophic
Trend: Stable
Created: 9/1/2020 12:27:55 PM
Updated: 10/15/2020 11:04:32 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

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

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

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

Agriculture

Source Confidence

Low

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-rivers

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 uses are assessed (monitored) as “not supported” due to the occurrence of aesthetically objectionable conditions caused by poor water transparency related to algal and non-algal turbidity. The Class BLW uses remain assessed (evaluated) as “partially supported” due to cyanobacteria blooms. Class HH uses are considered “fully assessed” based on fish tissue sampling.

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 2016-2017	21780001	Lake Manawa Beach (Lake Manawa State Park)
Iowa DNR	6	WQ	CY 2014-2018	22780003	Lake Manawa	Lake Deep Point
Iowa DNR		FT	See Below	66	Lake Manawa

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
21780001	6	20 / 2	44.97	9.5	NA	No	3	15%	NO	Monitored	Full

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
22780003	6	15 / 5	8.95	8.56	8.6	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
22780003	6	Chlorophyll a TSI	15 / 5	36	79	70	YES	Monitored	Not
22780003	6	Secchi TSI	15 / 5	65	93	75	YES	Monitored	Not
22780003	6	Total Phosphorus TSI	15 / 5	57	80	73	NA	NA	NA
22780003	6	Inorganic suspended solids	15 / 5	0.3	50	12	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
22780003	6	Ammonia	15 / 5	0.356	0.05	0.01	0 / 0	0% / 0%	NO	Monitored	Full
22780003	6	Dissolved oxygen	15 / 5	11.01	8.81	8.9	NA / 1	NA / 7%	NO	Monitored	Full
22780003	6	pH	15 / 5	8.95	8.56	8.6	0 / NA	0% / NA	NO	Monitored	Full
22780003	6	Temperature	15 / 5	30	25.34	25.5	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
22780003	6	11	609.904	97.9 %	86.754	83.6 %	YES	Evaluated	3b

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 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

7/29/15

channel catfish

fillet

<0.02

<0.06

0.02

Monitored

Full

8/26/15

largemouth bass

plug

0.050

Monitored

Full

Monitoring and Methods

Assessment Key Dates

6/17/2014

Fixed Monitoring Start Date

8/26/2018

Fixed Monitoring End Date

7/29/2015

Fish Tissue Monitoring

8/26/2015

Fish Tissue Monitoring

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