Crystal Lake IA 02-IOW-781

Hancock County S15T97NR25W at Crystal Lake.

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: Eutrophic
Trend: Stable
Created: 10/27/2025 3:09:39 PM
Updated: 11/13/2025 2:39:17 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

High

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

High

Cycle Added

2000

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

2000

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Fish Kill: Due To Natural Causes

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Natural: Ordinary Stratification and Bottom-Water Hypoxia/Anoxia

Source Confidence

Low

Cycle Added

2024

Impairment Rationale

Potential Impairment

Data Source

Fish kill investigation: Iowa DNR

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 aesthetically objectionable conditions caused by poor water transparency and nuisance blooms of algae. The Class BLW use was assessed (evaluated) as “WINOFI” due to a fish kill due to natural causes. The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data. Note: A TMDL for organic enrichment at Crystal Lake was prepared by DNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved). Because all of the Section 303(d) impairments identified for this assessment/listing cycle, it remains listed as Category 4a (TMDL approved) for this assessment/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 2020-2024	22410001	Crystal Lake Max Depth
Iowa DNR	6	FT	See Below	1290	Crystal Lake Wildlife Management Area

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
22410001	6	18 / 5	7.7	9.1	8.4	2	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
22410001	6	Chlorophyll a TSI	18 / 5	47	88	68	YES	MONITORED	NOT
22410001	6	Secchi TSI	18 / 5	42	77	68	YES	MONITORED	NOT
22410001	6	Total Phosphorus TSI	18 / 5	51	84	72	NA	NA	NA
22410001	6	Fixed suspended solids	18 / 5	0.7	20	6	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
22410001	6	Dissolved Oxygen	17 / 5	4	12.3	8.1	2	NA / NA	4	NO	MONITORED	FULL
22410001	6	pH	18 / 5	7.7	9.1	8.4	2	NA / NA	4	NO	MONITORED	FULL
22410001	6	Temperature	18 / 5	13.2	29.1	21.2	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
22410001	6	7	36.6237	89.23%	7.3181	44.69%	NO	EVALUATED	NA

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
22410001	6	Total suspended solids	18 / 5	1.5	39	18	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
22410001	6	Ammonia	18 / 5	0.78	0.13	0.06	0 / 0	NO	MONITORED	FULL

Class BLW - Fish Kill:

The Class BLW use was assessed (evaluated) as “WINOFI” based on results of a fish kill investigation in July of 2021. Because the cause of the fish kill was not identified, or the fish kill was attributed to a non-pollutant cause (e.g., winterkill), the assessment type is “evaluated.” Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of waters in need of further investigation. If no additional fish kills are reported in the segment for a 5 year period (2026), the Category will be changed from 3b to 3a (water not assessed).

Details about the 2021 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/888,https://programs.iowadnr.gov/fishkill/Events/1013

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
1290	tissue plug	2020	northern pike	2	66.4	0.156
1290	tissue plug	2020	walleye	1	51.1	0.223
1290	fillet	2024	common carp	3	44.0	0.022	<0.05	<0.0246
Support Level	Full

Monitoring and Methods

Assessment Key Dates

10/22/2024

Monitoring End

5/18/2020

Monitoring Start

10/28/2002

TMDL Completed

10/9/2024

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

7/1/2021

Fish Kill

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)