Black Hawk Lake IA 04-RAC-1134

Sac County S35T87NR36W at Lake View.

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: 8/13/2020 2:33:54 PM
Updated: 10/14/2020 11:49:24 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Turbidity

Support Level

Partially Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

High

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Algal Growth: Chlorophyll a

Support Level

Partially Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

High

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2016

Impairment Rationale

Single-sample maximum criterion exceeded in significantly > 10% of samples

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

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 “partially supporting” due to violations of the state water quality criteria for indicator bacteria, poor water clarity caused by algal and non-algal turbidity. The Class BLW uses are assessed (monitored) as “fully supported.” Class HH uses are assessed as “fully supported” based on fish tissue sampling. Note: The TMDL prepared by Iowa DNR for impairments due to algae and turbidity was approved by U.S.EPA in February 2012. Not all Section 303(d) impairments identified for the current assessment/listing cycle (indicator bacteria), however, are addressed in the TMDL. Thus, this waterbody remains in IR Category 5a (impaired; TMDL required) for this assessment/listing cycle.

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	21810001	Denison Beach (Black Hawk State Park)
Iowa DNR	6	WQ	CY 2016-2018	21810002	Black Hawk Campground Beach (Black Hawk St. Park)
Iowa DNR	6	WQ	CY 2014-2018	22810002	Black Hawk Lake	Lake Deep Point
Iowa DNR	6	WQ	CY 2014-2017	22810003	Black Hawk Lake West Arm	TMDL Sampling Point
Iowa DNR		FT	See Below	138	Black Hawk 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
21810001	6	46 / 3	114.31	80.02	126.08	Yes	13	28%	YES	Monitored	Partial
21810002	6	44 / 3	30.41	31.53	29.59	No	3	7%	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
22810002	6	15 / 5	9.2	8.5	8.4	2	13%	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
22810002	6	Chlorophyll a TSI	54 / 5	15	80	66	YES	Monitored	Not
22810003	6	Chlorophyll a TSI	11 / 4	31	78	64	NO	Monitored	Full
22810002	6	Secchi TSI	15 / 5	47	77	65	YES	Monitored	Not
22810002	6	Total Phosphorus TSI	54 / 5	47	105	76	NA	NA	NA
22810003	6	Total Phosphorus TSI	11 / 4	53	89	80	NA	NA	NA
22810002	6	Inorganic suspended solids	15 / 5	0.3	12.6	3.3	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
22810002	6	Ammonia	15 / 5	0.311	0.06	0.04	0 / 0	0% / 0%	NO	Monitored	Full
22810002	6	Dissolved oxygen	15 / 5	13.8	9.4	10.3	NA / 1	NA / 7%	NO	Monitored	Full
22810002	6	pH	15 / 5	9.2	8.5	8.4	2 / NA	13% / NA	NO	Monitored	Full
22810002	6	Temperature	15 / 5	27.1	22.4	23.9	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
22810002	6	11	90.528	100 %	1.404	6.4 %	NO	Evaluated	NA

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

138

8/26/15

channel catfish

fillet

<0.02

<0.06

0.04

Monitored

Full

138

8/26/15

walleye

plug

0.190

Monitored

Full

Note: A fishery renovation and lake drawdown was completed in 2012 to remove rough fish from Black Hawk Lake.

Monitoring and Methods

Assessment Key Dates

5/19/2014

Fixed Monitoring Start Date

8/27/2018

Fixed Monitoring End Date

8/26/2015

Fish Tissue Monitoring

2/1/2012

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