Tuttle Lake (a.k.a. Okamanpeedan Lake) IA 04-EDM-975

Emmett County S14T100NR32W 2 mi. N of Dolliver.

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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 10/27/2025 3:09:46 PM
Updated: 1/7/2026 10:14:45 AM

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

High

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

High

Cycle Added

2002

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Turbidity

Support Level

Not 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

2002

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains assessed as “not supported” due to very poor water transparency related to high levels of inorganic turbidity and algal blooms that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The Class BLW use remains assessed (monitored) as “fully supported.” All other designated uses remain “not assessed.” Note: A TMDL for algae and turbidity at Tuttle Lake was prepared by DNR and approved by EPA in 2005, and these impairments for this lake were thus moved to IR Category 4a for the current assessment and listing cycle.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2021	22320002	Tuttle Lake

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
22320002	6	14 / 3	8.36	9	8.66	0	4	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
22320002	6	Chlorophyll a TSI	15 / 3	44	73	70	YES	MONITORED	NOT
22320002	6	Secchi TSI	14 / 3	70	93	80	YES	MONITORED	NOT
22320002	6	Total Phosphorus TSI	15 / 3	63	95	75	NA	NA	NA
22320002	6	Inorganic suspended solids	5 / 1	2	32	3.3	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
22320002	6	Dissolved Oxygen	14 / 3	8.34	18.57	12.26	0	NA / NA	4	NO	MONITORED	FULL
22320002	6	pH	14 / 3	8.36	9	8.66	0	NA / NA	4	NO	MONITORED	FULL
22320002	6	Temperature	14 / 3	14.4	31.7	23.7	0	NA / NA	4	NO	MONITORED	FULL

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
22320002	6	Ammonia	6 / 2	0.23	0.1	0.08	0 / 0	NO	EVALUATED	FULL

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/14/2018

Monitoring Start

9/14/2021

Monitoring End

1/13/2005

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)