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 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

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Cycle: 2018
Release Status: Final
Overall IR: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trophic: Eutrophic
Trend: Stable
Created: 3/14/2019 1:00:18 PM
Updated: 4/22/2019 10:10:03 AM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

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

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

SUMMARY: The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to poor water quality caused by an exotic fish population (common carp). The Class C (drinking water) uses are assessed as “fully supported.” Fish consumption uses are assessed as "fully supporting". Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau, (3) IDNR RAFT fish tissue monitoring, and (4) results of the Iowa Voluntary Atrazine Monitoring Program from 2010-2012 by Syngenta Crop Protection, Inc.

Assessment Explanation

For the 2018assessment/listing cycle, the Class B(LW) (aquatic life) uses of Diamond Lake are assessed (evaluated) as “partially supported” based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 67, and 69 respectively for Diamond Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Diamond Lake in the Eutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.The data show no violations of the Class A1 criterion for pH in 15 samples.Although a Secchi depth and chlorophylla indexvaluesof 65 or greater suggests impairment of Class A (primary contact recreation) uses, this water supply reservoir is not designated for Class A (primary contact uses) in the Iowa Water Quality Standards

The level of inorganic suspended solids was relitivley low at Diamond Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Diamond Lake (8.3 mg/L) was ranked 114th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at Diamond Lake. These data show that cyanobacteria comprised 41% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (10 mg/L) was ranked 45th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the DNR Fisheries Bureau and results from the ISU lake surveys. Based on information from the DNR Fisheries Bureau,common carp are causing major water quality and fish quality problems in thislake.Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Diamond Lake.

The Class C (drinking water) uses are assessed (monitored) as “fully supported” based primarily on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from 2010-2012. The mean and median atrazine levels over this three-year period were 1.1 ug/l and 0.7 ug/L, respectively. The maximum value was 4.5 ug/l. None of the moving annual averages for atrazine for the years 2010 through 2012 at Diamond Lake exceeded the MCL (maximum average = 1.5 ug/l). Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported."The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. The results of the ISU surveys from 2012-2016 show that nitrate levels are extremely low at this lake (maximum value = 2.8 mg/l; median = 0 mg/l)and are well-below the MCL of 10 mg/l.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR fish contaminant (RAFT) monitoring at Diamond Lake in 2013.The composite samples of fillets from largemouth bass and channel catfish had low levels of contaminants.Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.124 ppm.Levels of primary contaminants in the composite sample of channel catfish fillets were as follows:total PCBs: <0.6 ppm; and technical chlordane: <0.2 ppm.The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2013 RAFT sampling conducted at this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.

Monitoring and Methods

Assessment Key Dates

6/18/2012

Fixed Monitoring Start Date

9/19/2016

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)