Backbone Lake IA 01-MAQ-20

Backbone Lake Dam to S Fk Maquoketa R. (S16 T90N R6W Delaware Co.)

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: Eutrophic
Trend: Stable
Created: 10/27/2025 3:09:25 PM
Updated: 1/5/2026 9:25:04 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2004

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Beach monitoring: Iowa DNR WQMA

TMDL Priority

Tier II

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "not supported" due to high levels of indicator bacteria. The Class BWW1 use was assessed as "Fully supported." 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 2023-2024	14000575	Backbone 1
Iowa DNR	6	WQ	CY 2023-2023	14000576	Backbone 2
Iowa DNR	6	WQ	CY 2023-2024	14000577	Backbone 3
Iowa DNR	6	WQ	CY 2022-2024	21280001	Backbone Beach

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2022/ 2023/2024)

2022 Geometric Mean

2023 Geometric Mean

2024 Geometric Mean

Violates Annual Geometric Mean?

# 2022 SSM violations / SSM Violations needed for impairment

# 2023 SSM violations / SSM Violations needed for impairment

# 2024 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

14000575

0/8/8

152

YES

2 / 3

3 / 3

YES

MONITORED

NOT

14000576

0/7/8

188

YES

1 / 3

3 / 3

YES

NOT

14000577

0/8/8

282

YES

1 / 3

4 / 3

YES

MONITORED

NOT

21280001

15/14/15

249

113

241

YES

9 / 4

4 / 4

7 / 4

YES

MONITORED

NOT

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
21280001	6	44 / 3	7.38	9.16	8.18	2	8	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
14000577	6	Secchi TSI	6 / 1	59	70	64	NO	EVALUATED	FULL

Class BWW1 - 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
21280001	6	Dissolved Oxygen	44 / 3	6.86	17.29	12.27	0	NA / NA	8	NO	MONITORED	FULL
21280001	6	pH	44 / 3	7.38	9.16	8.18	2	NA / NA	8	NO	MONITORED	FULL
21280001	6	Temperature	44 / 3	12.55	28.41	23.1	0	NA / NA	8	NO	MONITORED	FULL

Class HH: No Data

Monitoring and Methods

Assessment Key Dates

5/26/2021

Monitoring Start

9/24/2024

Monitoring End

Methods

200

Physical/Chemical Monitoring

420

Indicator bacteria monitoring