DRAFT 2026 assessment for Cedar Lake

Cedar Lake IA 02-CED-512

Linn County S21T83NR7W in Cedar Rapids.

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

5 - Water is impaired or threatened and a TMDL is needed.

Trophic

Hypereutrophic

Trend

Stable

Current Phase

Public Comment

Created

10/27/2025 3:10:30 PM by

Updated

11/12/2025 8:22:10 AM by

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2026

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier IV

Algal Growth: Cyanobacteria

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

303(d) Listing Status

New

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Low

Cycle Added

2026

Impairment Rationale

Potential Impairment

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Fully Supported

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BLW use was assessed (monitored) as “not supported” based on results of the Class BLW criterion for pH and was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. The Class HH (fish consumption) use was assessed as “fully supported” based on fish tissue sampling. Note: A TMDL for chlordane at Cedar Lake was prepared by DNR and approved by EPA in 2001. Subsequently, levels of chlordane in Cedar Lake fish have fallen well-below DNR/IDPH consumption advisory threshold.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2021-2024	14000413	Cedar Lake	Lake Deep Point
Iowa DNR	6	FT	See Below	1123	Cedar Lake

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
14000413	6	Dissolved Oxygen	12 / 4	4.8	15.6	10.1	1	NA / NA	4	NO	MONITORED	FULL
14000413	6	pH	12 / 4	7.79	9.44	8.76	5	NA / NA	4	YES	MONITORED	NOT
14000413	6	Temperature	12 / 4	16.2	28	24.6	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
14000413	6	4	191.5616	94.33%	77.634	57.11%	YES	EVALUATED	WINOFI

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
14000413	6	Ammonia	12 / 4	0.54	0.09	0.04	0 / 1	NO	MONITORED	FULL

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)
1123	fillet	2016	channel catfish	3	41.6	0.05	0.05	0.06
1123	tissue plug	2016	largemouth bass	5	37.8	0.05
Support Level	Full

Monitoring and Methods

Assessment Key Dates

8/18/2016

Fish Tissue Monitoring

8/17/2016

Fish Tissue Monitoring

6/14/2021

Monitoring Start

8/26/2024

Monitoring End

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)