Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010.
Basis for 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 “partially supported” due to violations of the Class A1,B(LW) criterion for pH. Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010.
Note: A TMDL for organic enrichment at Crystal Lake was prepared by IDNR 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 is suggested for de-listing for the 2012 assessment/listing cycle, and thus Crystal Lake is moved back to IR Category 4a (TMDL approved).
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Crystal Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (11 samples), 2009 (11 samples), and 2010 (11 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Crystal Lake beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 12 E. coli orgs/100 ml in 2008, 8 E. coli orgs/100 ml in 2009, and 8 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 9% in 2008, 0% in 2009 and 0% in 2010. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “full support” of the Class A1 uses. The Class A1 uses were assessed as "not supported" for the 2008 assessment/listing cycle due to violations of the geometric mean criterion. Based on IDNR's assessment methodology two consecutive assessment/listing cycles with no violations of the geometric mean criterion are necessary to propose de-listing of the bacteria impairment. Both the 2010 and the current (2012) assessments show no violations of the geometric mean criterion. Therefore the bacteria impairment at Crystal Lake is suggested for de-listing.
For the 2012 reporting cycle, the Class A1 (primary contact recreation) uses for Crystal Lake are also assessed as “not supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. Using the median values from these surveys from 2006 through 2010 (approximately 19 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 71, 69, and 76 respectively for Crystal Lake. According to Carlson (1977) the index values for Secchi depth and total phosphorus place Crystal Lake in the hypereutrophic category while the value for chlorophyll a places Crystal Lake in between the eutrophic and hypereutrophic categories. These values suggest 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 levels of inorganic suspended solids at this lake were very high and suggest that non-algal turbidity contributes to the impairment at Crystal Lake. The median level of inorganic suspended solids in Crystal Lake (12.0 mg/L) was the 13th highest median of the 134 lakes sampled by the ISU and UHL surveys.
Data from the 2006-2010 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Crystal Lake. These data show that cyanobacteria comprised only 30% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.9 mg/L) was the 37th lowest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses for Crystal Lake are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH. The data for pH show 7 violations of the Class A1,B(LW) criterion for pH in 19 samples (37%). Based on IDNR’s assessment methodology, these violations are significantly greater than 10% of the samples and therefore constitute an impairment (partial support/monitored) of the Class B(LW) uses of Crystal Lake. Results from the ISU and UHL lake surveys from 2006-2010 show no violations of the Class B(LW) criterion for dissolved oxygen in 19 samples or ammonia in 18 samples.
In addition a fish kill occurred at Crystal Lake 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.
According to IDNR’s 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.” This is the same assessment as was developed for the 2010 Integrated Report. If a cause of the kill was not identified during the IDNR 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 2b of Iowa’s 2012 Integrated Report.
Note: A hydraulic dredging project was completed in 2007 that should reduce suspended sediment and turbidity problems. IDNR 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.
Fish consumption remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.
