Black Pit IA 02-WIN-1920

Mason City T96N R20W Sec17 NE and T96N R20W Sec8 SE Cerro Gordo Co.

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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

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Cycle: 2022
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trophic: Unknown
Trend: Unknown
Created: 1/5/2022 7:30:37 AM
Updated: 2/1/2022 7:18:20 AM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Fish Kill: Caused By Other

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

2016

Impairment Rationale

Non Pollutant-caused fish kill

Data Source

Fish kill investigation: Iowa DNR

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

This lake is not designated for Class A1 use. The Class BLW use was assessed (evaluated) as “WINOFI” due to a fish kill investigation. 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 2018-2020	22170003	Black Pit

Class BLW - Conventional 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
22170003	6	Ammonia	9 / 3	0.0024	0.5055	0.13	NA	0 / 0	3	NO	Evaluated	Full
22170003	6	Dissolved Oxygen	9 / 3	3.1	16.1	9.6	1	NA / NA	3	NO	Evaluated	Full
22170003	6	pH	9 / 3	7.5	8.7	7.9	0	NA / NA	3	NO	Evaluated	Full
22170003	6	Temperature	9 / 3	17.6	26.6	21.1	0	NA / NA	3	NO	Evaluated	Full

Class BLW - Fish Kill:

The Class BLW use was assessed (evaluated) as “WINOFI” due to a fish kill that occurred in July of 2015. 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 10 year period, the Category will be changed from 3b to 3a (water not assessed).

Details about the 2015 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/886

Class HH: No Data

Additional Information: 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
22170003	6	Chlorophyll a TSI	9 / 3	42	76	56	NA	NA	NA
22170003	6	Secchi TSI	9 / 3	50	93	63	NA	NA	NA
22170003	6	Total Phosphorus TSI	9 / 3	56	85	71	NA	NA	NA
22170003	6	Inorganic suspended solids	9 / 3	0.6	73.7	3	NA	NA	NA

Monitoring and Methods

Assessment Key Dates

9/14/2020

Non-fixed Monitoring End Date

6/4/2018

Non-fixed Monitoring Start Date

7/11/2015

Fish Kill

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

222

Non-fixed-station monitoring (conventional during key seasons and flows)