East Twin Lake IA 02-IOW-777

Hancock County S29T94NR24W 3 mi. E of Kanawha.

This is a DRAFT assessment

Draft assessments may change without notice

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 2022 - 2024
Stream/River Water Quality Data	CY 2022 - 2024
Lake Water Quality Data	CY 2020 - 2024
Biological Sampling Data	CY 2020 - 2024*
Fish Kill Data	CY 2020 - 2024
Fish Tissue Sampling Data	CY 2020 - 2024
Continuous Dissolved Oxygen Sampling Data	CY 2020 - 2024
*Biological sites sampled in both 2019 and 2023 were also assessed.

Open Segment Map
View 2026 assessment summary page

Cycle: 2026
Current Phase: Public Comment
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Hypereutrophic
Trend: Unknown
Created: 10/27/2025 3:11:39 PM
Updated: 1/12/2026 11:08:41 AM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2024

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-shallow lakes & wetlands

TMDL Priority

Tier IV

Turbidity: Suspended Solids

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-shallow lakes & wetlands

TMDL Priority

Tier IV

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2026

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-shallow lakes & wetlands

TMDL Priority

Tier III

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BLW use was assessed (monitored) as "not supported" due to high levels of total suspended solids that leads to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life and violations of the Class BLW criterion for pH. High levels of algae at this shallow lake also suggest impairment due to aesthetically objectionable conditions. All other designated uses were “not assessed.”

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2020-2024	14000289	East Twin Lake

Class BLW – Shallow Lake TSI:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation?	Assessment Type	Support Level
14000289	6	Chlorophyll a TSI	21 / 5	44	101	76	YES	MONITORED	NOT

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
14000289	6	Dissolved Oxygen	20 / 5	5.55	15.35	11.23	0	NA / NA	5	NO	MONITORED	FULL
14000289	6	pH	16 / 4	8.15	9.59	8.81	5	NA / NA	4	YES	MONITORED	NOT
14000289	6	Temperature	20 / 5	11.5	28.1	19.3	0	NA / NA	5	NO	MONITORED	FULL

Class BLW - Protection of Submerged Aquatic Vegetation:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median Value >= SAV	Assessment Type	Support Level
14000289	6	Total suspended solids	21 / 5	2	180	42	YES	MONITORED	NOT

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
14000289	6	Ammonia	8 / 3	0.1	0.04	0.02	0 / 0	NO	EVALUATED	FULL

Class HH - No Data

In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.

Monitoring and Methods

Assessment Key Dates

5/18/2020

Monitoring Start

9/4/2024

Monitoring End

Methods

200

Physical/Chemical Monitoring