Iowa DNR
Iowa DNR
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Water Quality Assessments
Impaired Waters List

Crystal Lake IA 02-IOW-781

Hancock County S15T97NR25W at Crystal Lake.

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Cycle
2018
Release Status
Final
Overall IR
4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic
Hypereutrophic
Trend
Stable
Created
3/14/2019 12:39:52 PM
Updated
2/24/2020 8:59:39 AM
Use Support
Class A1
Recreation - Primary contact
Not Supported
Support Level
Not Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
High
Status
Continuing
Source
Natural: Internal Nutrient Recycling (Primarily Lakes)
Source Confidence
High
Cycle Added
2000
Impairment Rationale
Narrative criteria violation: aesthetically objectionable conditions
Data Source
Ambient monitoring: Iowa DNR-lakes
Support Level
Not Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
High
Status
Continuing
Source
Other: Sediment Resuspension
Source Confidence
High
Cycle Added
2000
Impairment Rationale
Narrative criteria violation: aesthetically objectionable conditions
Data Source
Ambient monitoring: Iowa DNR-lakes
Support Level
Not Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
Slight
Status
Continuing
Source
Natural: Internal Nutrient Recycling (Primarily Lakes)
Source Confidence
Moderate
Cycle Added
2008
Impairment Rationale
Significantly > 10% of samples fail to meet criterion
Data Source
Ambient monitoring: Iowa DNR-lakes
Class BLW
Aquatic Life - Lakes and wetlands
Not Supported
Support Level
Not Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
Slight
Status
Continuing
Source
Natural: Internal Nutrient Recycling (Primarily Lakes)
Source Confidence
Moderate
Cycle Added
2008
Impairment Rationale
Significantly > 10% of samples fail to meet criterion
Data Source
Ambient monitoring: Iowa DNR-lakes
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
Moderate
Cycle Added
2010
Impairment Rationale
Non Pollutant-caused fish kill
Data Source
Fish kill investigation: Iowa DNR
Support Level
Further Investigation Needed
Impairment Code
3b - Use potentially impaired based on an evaluated assessment.
Cause Magnitude
Moderate
Status
Continuing
Source
Natural: Ordinary Stratification and Bottom-Water Hypoxia/Anoxia
Source Confidence
Moderate
Cycle Added
2016
Impairment Rationale
Non Pollutant-caused fish kill
Data Source
Fish kill investigation: Iowa DNR
Support Level
Further Investigation Needed
Impairment Code
3b - Use potentially impaired based on an evaluated assessment.
Cause Magnitude
Slight
Status
New
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2018
Impairment Rationale
Adverse impacts on plant/animal communities
Data Source
Ambient monitoring: Iowa DNR-lakes
Class HH
Human Health -
Not Assessed
General Use
General Use water -
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of the Class A1,B(LW) criterion for pH, and aesthetically objectionable conditions caused by poor water transparency and nuisance blooms of algae. The Class B(LW) (aquatic life) uses are assessed (monitored) as “not supported” due to violations of the Class A1,B(LW) criterion for pH and multiple fish kills due to natural causes. Fish consumption uses remain “not assessed.” 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.

Assessment Explanation

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Crystal Lake are assessed (monitored) as "not supported" due to poor water transparency, aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH 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 70, 72, and 80 respectively for Crystal Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Crystal Lake in the Hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column. The data show 5 violations of the Class A1 criterion for pH in 15 samples (33%).

The level of inorganic suspended solids was low at Crystal Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Crystal Lake (1.6 mg/L) was ranked 9th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a large population of cyanobacteria exists at Crystal Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 90% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (39.6 mg/L) was ranked 104th of the 138 lakes sampled. This median is in the worst 25% of the 138 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa's narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2012-2016. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. Assessments based on the level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on results of a fish kill investigation in August 2009 and another in Octoberof 2015. The first kill occurred on or before August 28, 2009. Thousands of dead minnows were found in the lake. The kill was attributed to natural causes (=summer kill) due to an algae bloom and low dissolved oxygen. The second kill occurred on or before July 9, 2015. An estimated 1,000 fish were killed. No estimates of the value of the fish killed or the cost of the Iowa DNR investigation were provided. Similar to other recent kills, the cause of the kill was attributed to "summer kill/low DO". The thirdkill occurred on or before October22, 2015. Thousands of fish of unknown types were found dead. The kill was also attributed to natural causes (=summer kill) due to an algae bloom die off resulting in low dissolved oxygen conditions.According to the DNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2008-2011) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.”If a cause of the kill was not identified during the DNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.”Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.Thus, this assessment segment will remain in Category 3b of Iowa’s 2012 Integrated Report.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "not supported" due to violations of the Class A1,B(LW) criterion for pH. Results of the ISU lake survey from2012-2016show there were no violations of the criterion for ammonia in 15 samples(0%), 2 violations of the criterion for dissolved oxygen in 15 samples(13%), and 5 violations of the criterion for pH in 15 samples(33%). Based on DNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Crystal Lake.

Fish consumption remains "not assessed" due to the lack of recent fish contaminant monitoring at this lake.

Note:A TMDL for organic enrichment at Crystal Lake was prepared by DNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 and 2006 assessment/listing cycles.Because not all of the Section 303(d) impairments identified for the 2008 and 2010 assessment/listing cycle (indicator bacteria) were addressed by the TMDL, this waterbody was placed in IR category 5a (TMDL needed) for the 2008 and 2010 assessment/listing cycles. Due to a decrease in indicator bacteria at Crystal Lake, the bacteria impairment was suggested for de-listing for the 2012 assessment/listing cycle, and thus Crystal Lake was moved back to IR Category 4a (TMDL approved).It remains listed as Category 4a (TMDL approved) for the 2018 assessment/listing cycle.

Note: A hydraulic dredging project was completed in 2007 that should reduce suspended sediment and turbidity problems. DNR Fisheries staff also did a complete fisheries renovation in 2008 to remove common carp and black bullhead and create a desirable fishery. This will also likely reduce sediment and turbidity problems.

Monitoring and Methods
Assessment Key Dates
6/6/2012
Fixed Monitoring Start Date
9/5/2016
Fixed Monitoring End Date
8/28/2009
Fish Kill
10/28/2002
Fixed Monitoring Start Date
10/22/2015
Fish Kill
7/9/2015
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)
340
Primary producer surveys (phytoplankton/periphyton/macrophyton)