Big Lake (incl Gilbert's Pond) IA 06-WEM-1712

Pottawattamie County S14T75NR44W N edge Council Bluffs

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.

Open Segment Map
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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: 1/6/2022 1:26:54 PM
Updated: 2/2/2022 1:47:26 PM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Fish Kill: Cause Unknown

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Natural

Source Confidence

Low

Cycle Added

2018

Impairment Rationale

Potential Impairment

Data Source

Fish kill investigation: Iowa DNR

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BLW use was assessed (evaluated) as “WINOFI” based on results of a fish kill investigation in July 2012. All other designated uses were “not assessed.”

Assessment Explanation

Class BLW - Fish Kill:

The Class BLW use was assessed (evaluated) as “WINOFI” due to fish kills that occurred in July of 2012. 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 2011 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/866

Class HH - Fish Tissue sampling: No Data

Monitoring and Methods

Assessment Key Dates

7/18/2012

Fish Kill

Methods

140

Incidence of spills and/or fish kills