Diamond Lake IA 03-NSK-861

Poweshiek County S2T78NR15W approx 2.5 mi SW of Montezuma.

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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 7/29/2020 1:15:18 PM
Updated: 10/13/2020 1:36:09 PM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

Partially Supported

Exotic/Invasive Species: Fish Species

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Other: Exotic Species

Source Confidence

Moderate

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Algal Growth: Chlorophyll a

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

New

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-shallow lakes & wetlands

TMDL Priority

Tier I

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BLW use is assessed as “partially supported” due to poor water quality caused by an exotic fish population (common carp). High levels of algae at this wetland also suggest impairment due to aesthetically objectionable conditions. The Class C use is assessed as “fully supported.” The Class HH use remains assessed as "fully supporting" based on fish tissue sampling.

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2014-2018	22790005	Diamond Lake
Iowa DNR		FT	See Below	294	Diamond Lake

Class BLW - TSI's

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation	Assessment Type	Support Level
22790005	6	Chlorophyll a TSI	15 / 5	44	74	65	YES	Monitored	Not
22790005	6	Inorganic suspended solids	15 / 5	2.4	40.3	8.3	NA	NA	NA

The TSI value for Secchi depth is not used to evaluate the attainment of aquatic life goals in shallow lakes. Due to the depth of these shallow lakes, TSI values for Secchi depth can be misleading. In some instances, the Secchi disk remains visible at the bottom of the lake and the depth of the lake is recorded as the Secchi depth. In these instances, water clarity may be sufficient to support the Class B(LW) uses, but the index value is limited by the depth of the lake. Thus the combination of total suspended solids and chlorophyll a will be used to determine whether or not the Class B(LW) uses are impaired in these shallow systems.

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
22790005	6	Ammonia	15 / 5	0.649	0.16	0.09	0 / 0	0% / 0%	NO	Monitored	Full
22790005	6	Dissolved oxygen	15 / 5	11.77	8.14	8.8	NA / 1	NA / 7%	NO	Monitored	Full
22790005	6	pH	15 / 5	8.8	8.2	8.3	0 / NA	0% / NA	NO	Monitored	Full
22790005	6	Temperature	15 / 5	28.8	23.54	23.6	0 / 0	0% / 0%	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 Wet Mass = 75th Percentile	Assessment Type	Support Level
22790005	6	11	22.945	81.9 %	8.300	35.1 %	NO	Evaluated	NA

Class BLW - Protection of Submerged Aquatic Vegetation:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median Value >= SAV	Assessment Type	Support Level
22790005	6	Total suspended solids	15 / 5	8	48	19	NO	Monitored	Full

Guidelines for wetland assessment from the Upper Mississippi River Conservation Committee’s Water Quality Technical Section (2003) state that an average total suspended solids concentration during the growing season of less than 30 mg/L is necessary to provide sufficient water clarity to support the growth of submersed aquatic vegetation in wetlands and shallow lakes. High levels of total suspended solids impede the growth of submersed aquatic vegetation (SAV). Submersed aquatic vegetation is critical to the health of wetland and shallow lake ecosystems. The elimination of SAV can degrade habitat quality such that undesirable aquatic species such as cyanobacteria, common carp and fathead minnows dominate. As such, the suppression of SAV constitutes a violation of Iowa’s narrative water quality criteria protecting against undesirable or nuisance aquatic life.

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22790005	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	2.2	0.44	0.04	0	0%	NO	Monitored	Full

Class HH – Fish Tissue sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation?

PCBs result

PCBs violation?

Hg result

Hg violation?

Assessment Type

Support Level

294

7/31/13

channel catfish

fillet

<0.2

<0.6

0.05

Evaluated

Full

294

7/31/13

largemouth bass

plug

0.124

Evaluated

Full

Monitoring and Methods

Assessment Key Dates

6/23/2014

Fixed Monitoring Start Date

9/9/2018

Fixed Monitoring End Date

7/31/2013

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

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

260

Fish tissue analysis

270

PWS chemical monitoring (ambient water)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)