DRAFT 2026 assessment for Lake Icaria

Lake Icaria IA 05-NOD-1398

Adams County S10T72NR34W 4 mi N of Corning.

This is a DRAFT assessment

Draft assessments may change without notice

2026
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

Overall IR

1 - All designated uses are met.

Trophic

Eutrophic

Trend

Improving

Trend Comment

The turbidity impairment were removed this cycle for both the Class A1 and Class BLW

Current Phase

Public Comment

Created

10/27/2025 3:10:15 PM by

Updated

1/2/2026 10:45:23 AM by

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Fully Supported

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "fully supported". The Class BLW use is assessed as "fully supported." The Class C use was assessed (monitored) as “fully supported” based on water quality monitoring data and drinking water compliance monitoring required by the DNR. The Class HH (fish consumption) use was assessed (monitored) as "fully supported" based on fish tissue sampling data. Note: A TMDL for siltation at Lake Icaria was prepared by DNR and approved by EPA in 2003. Since all impairments for Lake Icaria were addressed in the TMDL, it will be listed as Category 4a for the current 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	22020001	Lake Icaria
Iowa DNR	6	FT	See Below	1059	Lake Icaria

Class A - 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
22020001	6	15 / 5	7.77	8.62	8.1	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
22020001	6	Chlorophyll a TSI	15 / 5	42	74	64	NO	MONITORED	FULL
22020001	6	Secchi TSI	15 / 5	51	77	63	NO	MONITORED	FULL
22020001	6	Total Phosphorus TSI	15 / 5	49	69	61	NA	NA	NA
22020001	6	Fixed suspended solids	15 / 5	1.7	16	3	NA	NA	NA

DNR's assessment methodology indicates that a TSI value less than or equal to 63 are necessary to suggest removal of an impairment. The Secchi depth TSI value for the 2014 assessment listing cycle was 66, which based on DNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions. Because the TSI value for the 2026 assessment/listing cycle is less than or equal to the delisting trigger of 63 (median TSI value for Secchi depth was 63), based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (5a) for Secchi depth is suggested for removal from category 4 for the 2026 assessment/listing cycle.

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
22020001	6	Dissolved Oxygen	15 / 5	3.9	8.2	6.6	2	NA / NA	4	NO	MONITORED	FULL
22020001	6	pH	15 / 5	7.77	8.62	8.1	0	NA / NA	4	NO	MONITORED	FULL
22020001	6	Temperature	15 / 5	18.2	29.1	23.9	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
22020001	6	5	29.47195855	96.99%	0.899667439	57.41%	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
22020001	6	Ammonia	15 / 5	0.352	0.13	0.1	0 / 0	NO	MONITORED	FULL

Class C - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22020001	6	Inorganic nitrogen (nitrate and nitrite)	14 / 5	0.03	1.74	0.5	0.23	0	NO	MONITORED	FULL
22020001	6	pH	15 / 5	7.77	8.62	8.1	8.1	0	NO	MONITORED	FULL

Class C - Iowa Drinking Water Compliance Report:

Compliance monitoring required by the Iowa DNR Water Supply Operations and Engineering Sections did not show violations of finished water caused by source water at the Corning Muni Water Department facility during the 2022-24 monitoring period. The results of compliance monitoring as reported in annual compliance reports are available at the following location at the Iowa DNR’s home page: https://www.iowadnr.gov/Environmental-Protection/Water-Quality/Water-Supply-Engineering/Annual-Compliance-Report.

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)
1059	tissue plug	2020	channel catfish	20	53.1	0.123
1059	tissue plug	2020	common carp	20	54.8	0.099
1059	tissue plug	2019	largemouth bass	10	32.1	0.083
1059	tissue plug	2020	walleye	5	49.2	0.153
1059	tissue plug	2019	walleye	5	50.5	0.136
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/3/2020

Monitoring Start

9/30/2024

Monitoring End

1/30/2003

TMDL Completed

7/1/2019

Fish Tissue Monitoring

7/1/2020

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

200

Physical/Chemical Monitoring

260

Fish tissue analysis

275

Drinking water compliance reports

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)