Arrowhead Pond IA 06-WED-1702

Pottawattamie County S29T77NR41W 1.5 mi SE of Neola

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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2022
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Stable
Created: 1/4/2022 1:27:19 PM
Updated: 3/24/2022 2:03:08 PM

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

Delisted

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Cycle Delisted

2022

Delisting Rationale

TMDL preparation and approval

Data Source

Ambient monitoring: Iowa DNR-lakes

Turbidity: Secchi Disk Transparency

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2006

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Turbidity: Suspended Solids

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2006

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "not supported" due to poor water transparency and algae blooms. The Class BLW use was assessed (evaluated) as “WINOFI” due to sediment and turbidity concerns at this lake. All other designated uses were “not assessed.” Note: A TMDL for siltation at Arrowhead Pond was prepared by DNR and approved by EPA in 2001. Additionally, a TMDL for algae at Arrowhead Pond was prepared by DNR and approved by EPA in 2020. All Section 303(d) impairments identified for the current assessment/listing cycle are addressed in the TMDL.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2019	22780002	Arrowhead Lake (Pottawatamie)

Class A1 - Indicator Bacteria: No Data

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
22780002	6	11 / 4	7.5	8.5	8	0	3	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
22780002	6	Chlorophyll a TSI	12 / 4	29	74	61	NO	Monitored	Full
22780002	6	Secchi TSI	12 / 4	43	78	67	YES	Monitored	Not
22780002	6	Total Phosphorus TSI	12 / 4	53	83	72	NA	NA	NA
22780002	6	Inorganic suspended solids	12 / 4	0.3	21	2	NA	NA	NA

Although the index value for Chlorophyll a was below the impairment trigger of 65 for this assessment cycle, the Class A1 use of Arrowhead Lake remains "not supported" due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Arrowhead Lake will remain listed as "not supported" for the 2022 assessment/listing cycle.

Class BLW - Conventional 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
22780002	6	Ammonia	11 / 4	0.008	0.355	0.12	NA	0 / 0	3	NO	Monitored	Full
22780002	6	Dissolved Oxygen	12 / 4	3.6	12.5	8.3	2	NA / NA	4	NO	Monitored	Full
22780002	6	pH	11 / 4	7.5	8.5	8	0	NA / NA	3	NO	Monitored	Full
22780002	6	Temperature	12 / 4	20.5	27.9	24.4	0	NA / NA	4	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 Concentration = 75th Percentile	Assessment Type	Support Level
22780002	6	5	58.07	96.7%	2.72	13.1%	NO	Evaluated	NA

Class HH: No Data

Monitoring and Methods

Assessment Key Dates

6/15/2016

Non-fixed Monitoring Start Date

9/10/2019

Non-fixed Monitoring End Date

1/28/2002

TMDL Completed

Methods

222

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)