Lake Pahoja IA 06-BSR-1532

Lyon County S23T99NR48W 5 mi SSW of Larchwood.

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
View assessment methodology in new window

Cycle: 2024
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 11/1/2023 8:13:29 AM
Updated: 2/5/2024 10:38:33 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Geometric mean criterion exceeded

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

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to violations of the state water quality criteria for indicator bacteria. The Class BLW use was assessed (monitored) as "fully supported." All other designated uses are “not assessed.” NOTE: A TMDL for impairments at Lake Pahoja due to algae and pH was prepared by Iowa DNR and approved by the U.S. EPA in 2018. Because not all of the impairments are covered by the TMDL for the current assessment cycle (indicator bacteria) the waterbody is placed in IR Category 5a (impaired and TMDL required.)

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2022	22600001	Lake Pahoja

Class A1 - Indicator Bacteria: No Data. See 2018 assessment for indicator bacteria impairment.

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
22600001	6	12 / 4	7.7	9.4	8.4	2	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
22600001	6	Chlorophyll a TSI	12 / 4	41	83	66	YES	Mon	Not
22600001	6	Secchi TSI	12 / 4	39	88	72	YES	Mon	Not
22600001	6	Total Phosphorus TSI	12 / 4	56	94	80	NA	NA	NA
22600001	6	Inorganic suspended solids	12 / 4	0.6	42	3.5	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
22600001	6	Dissolved Oxygen	12 / 4	4.6	11.8	7.7	1	NA / NA	4	NO	Mon	Full
22600001	6	pH	12 / 4	7.7	9.4	8.4	2	NA / NA	4	NO	Mon	Full
22600001	6	Temperature	12 / 4	14.8	26.7	21.9	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
22600001	6	3	11.77417904	87%	0.000947778	0%	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
22600001	6	Ammonia	12 / 4	0.313	0.07	0.04	0 / 1	NO	Mon	Full

Class BLW - Fish Kill Assessment: The Class BLW aquatic life use assessment based on the 2011 fish kill for this segment has been changed from 3b to 3a (not assessed) based on the age of the data.

Class HH - No Data: The previous assessment of full support has been removed due to the age of the data.

Monitoring and Methods

Assessment Key Dates

5/29/2018

Monitoring Start

9/12/2022

Monitoring End

9/26/2012

Fish Tissue Monitoring

9/22/2016

TMDL Completed

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring