Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program in 2004, 2005, and 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to (1) violations of the Class A1 criterion for indicator bacteria, (2) violations of the Class A1,B(LW) criterion for pH, and (3) 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. Also, violations of the Class B(LW) chronic criteria for ammonia suggest a potential impairment of the aquatic life uses. Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program in 2004, 2005, and 2006.
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 assessment/listing cycle (indicator bacteria) are addressed by the TMDL, this waterbody is placed in IR category 5a (TMDL needed) for the 2008 assessment/listing cycle.
EXPLANATION: Results of IDNR county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (monitored) as "not supported." Levels of indicator bacteria at Crystal Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (15 samples), 2005 (15 samples), and 2006 (16 samples) as part of the IDNR county 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) all thirty-day geometric means for 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 5-sample, 30-day 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).
At Crystal Lake beach, the geometric means of 2 thirty-day periods during the summer recreation season of 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. No geometric means violated this criterion in 2005 or 2006. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was less than 10% in the all of following recreation seasons: 2004: 7%, 2005: 0%, 2006: 6%. According to IDNR’s assessment methodology and U.S. EPA guidelines, the geometric mean violations suggest impairment of the Class A1 (primary contact recreation) uses.
For the 2008 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 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 75, 74, and 83 respectively for Crystal Lake. According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus 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 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 (20 mg/L) was the 6th highest median of the 132 lakes sampled by the ISU and UHL surveys.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Crystal Lake, which contributes to impairment at this lake. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (103.5 mg/L) was also the 6th highest of the 132 lakes sampled. This median is in the worst 25% of the 132 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 for the 2002-2006 period. 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. The assessment category for assessments based on 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 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 11 violations of the Class A1,B(LW) criterion for pH in 23 samples (48%). 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 2002-2006 show no violations of the Class B(LW) criterion for dissolved oxygen in 22 samples.
Results from the ISU and UHL lake surveys show 2 violations of the Class B(LW) criterion for ammonia in 16 samples. Based on IDNR’s 2008 Section 303(d) listing methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s chronic criterion for ammonia and thus do not suggest an impairment of the Class B(LW) aquatic life uses. Because, however, more than one violation of the chronic criterion for ammonia occurred, this potential impairment will be added to Iowa's list of waters in need of further investigation. Note: Based on consultation with other Region 7 states and U.S. EPA Region 7 staff in 2007, IDNR's methodology for assessing impairments due to violations of chronic criteria for toxic parameters (e.g., ammonia and toxic metals) was changed. Prior to the 2008 listing cycle, IDNR followed a U.S. EPA recommendation (U.S. EPA 1997b, page 3-18) that more than one violation of a water quality criterion for a toxic pollutant in an abundant data set indicates an impairment of aquatic life uses. Because no state in Region 7 collects ambient data with the frequency necessary to accurately identify compliance with a chronic criterion (i.e., to allow calculation of a short-term (4-day or 30-day averages)), Region 7 states concluded that another assessment approach (e.g., the 10% rule) was more appropriate. Thus, for the 2008 listing cycle, IDNR identified aquatic life impairments for toxic parameters when significantly more than 10% of the samples exceeded a chronic criterion.
Note: A hydraulic dredging project was completed in 2007 that should reduce suspended sediment and turbidity problems. IDNR Fisheries staff are also considering a complete fisheries renovation in 2008 to remove common carp and black bullhead, which would also likely reduce sediment and turbidity problems.
Fish consumption remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.
