Lake Ahquabi IA 04-LDM-1080

Warren County S14T75NR24W 4 mi SSW of Indianola.

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: Eutrophic
Trend: Stable
Created: 8/12/2020 3:28:01 PM
Updated: 10/14/2020 11:41:26 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2012

Impairment Rationale

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

Data Source

Beach monitoring: Iowa DNR WQMA

TMDL Priority

Tier II

Algal Growth: Chlorophyll a

Support Level

Partially Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2008

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

Not Assessed

Class HH

Human Health -

Not Assessed

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 supported” due to aesthetically objectionable conditions caused by algal turbidity and violations of the state's criteria for indicator bacteria. The Class BLW uses are assessed (monitored) as “fully supported.” The Class C (drinking water) uses are “not assessed” due to lack of enough information to base an assessment on. All other designated uses are “not assessed.”

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	21910001	Lake Ahquabi Beach (Lake Ahquabi State Park)
Iowa DNR	6	WQ	CY 2014-2018	22910002	Lake Ahquabi

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
21910001	6	15 / 3	15.15	5.0	5.0	NO	0	0%	NO	Monitored	Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Lake Ahquabi will remain listed for the 2020 cycle as "partially supported" its Class A1 uses due to indicator bacteria.

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
22910002	6	15 / 5	8.9	8.3	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
22910002	6	Chlorophyll a TSI	15 / 5	15	71	58	NO	Monitored	Full
22910002	6	Secchi TSI	15 / 5	41	77	63	NO	Monitored	Full
22910002	6	Total Phosphorus TSI	15 / 5	56	66	63	NA	NA	NA
22910002	6	Inorganic suspended solids	15 / 5	0.6	29	3	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Lake Ahquabi was listed as partially supporting its Class A1 uses 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, Lake Ahquabi will remain listed as "not supported" for the 2020 assessment/listing cycle.

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
22910002	6	Ammonia	15 / 5	0.19	0.04	0.01	0 / 0	0% / 0%	NO	Monitored	Full
22910002	6	Dissolved oxygen	15 / 5	10.9	8	8.7	NA / 2	NA / 13%	NO	Monitored	Full
22910002	6	pH	15 / 5	8.9	8.3	8.4	0 / NA	0% / NA	NO	Monitored	Full
22910002	6	Temperature	15 / 5	30.8	24	24.5	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
22910002	6	11	33.764	95.4 %	13.465	80 %	NO	Evaluated	NA

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22910002	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	0.035	0.027	0.03	0	0%	NO	Monitored	Full

The Class C uses are not assessed due to the lack of data sufficient for developing a valid assessment of support of the Class C uses.

Class HH - Fish Tissue Sampling data was removed based on the age of the data.

Monitoring and Methods

Assessment Key Dates

5/27/2014

Fixed Monitoring Start Date

8/29/2018

Fixed Monitoring End Date

8/21/2007

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring