Assessment Comments
Assessment is based on results of (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted from 2006-08 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses of the Red Rock Reservoir were assessed (monitored) as "not supported” due to violations of the state water quality standard for indicator bacteria. Occasional blooms of algae during summer months also remain a concern. The Class B(WW-1) (aquatic life) uses are assessed (monitored) as "fully supported" although sediment loading and a large population of common carp remain concerns at this lake. Fish consumption uses were assessed (monitored) as "fully supported" based on ACOE-sponsored annual fish contaminant monitoring from 2006-08. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted from 2006-08 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
EXPLANATION: Results of bacteria monitoring at the ISU/ACOE long-term station on the main reservoir near the dam suggest that the Class A1 uses should be assessed (monitored) as "fully supporting." The geometric mean level of indicator bacteria (E. coli) in the 34 samples collected at this station during the recreational seasons of 2006 through 2008 (2 orgs/100ml) is well below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Also, none of the 34 samples exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml (maximum sample value = 30 orgs/100 ml).
Results of ACOE beach monitoring at White Breast and North Overlook beaches from 2006 through 2008, however, suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at White Breast beach were monitored approximately three times per month during the primary contact recreation seasons (May through September) of 2006 (13 samples), 2007 (8 samples), and 2008 (8 samples) as part of the ACOE 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 White Breast beach, the geometric means of all 6 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in 2006: 23% or 2008: 0%. However, the percentage of samples exceeding Iowa's single-sample maximum criterion was significantly greater than 10% in 2007 (50%). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest the Class A1 uses should be assessed as "partially supported."
Results of ACOE beach monitoring at North Overlook beach from 2006 through 2008 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at North Overlook beach were monitored approximately three times per month during the primary contact recreation seasons (May through September) of 2006 (13 samples), 2007 (8 samples), and 2008 (7 samples) as part of the ACOE monitoring program. At North Overlook beach, the geometric means of 2 thirty-day periods during the summer recreation season of 2007 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. None of the geometric means exceeded the criteria in 2006 or 2008. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in any of the following recreation seasons: 2006: 8% and 2007: 25%, and 2008: 0%. According to IDNR’s assessment methodology and U.S. EPA guidelines, the exceedences of the geometric mean criterion suggest impairment of the Class A1 (primary contact recreation) uses.
Results of water quality monitoring at the ISU/ACOE long-term station on the main reservoir near the dam suggest that the Class A1 uses should be assessed (monitored) as "fully supporting." Using the median values from this survey from May through September of 2006 through 2008 (approximately 38 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus are 64, 60, and 75, respectively. According to Carlson (1977), the index value for total phosphorus places this reservoir in the hypereutrophic category, the index values for chlorophyll a places this reservoir in the eutrophic category, and the Secchi depth value places this reservoir in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and extremely high levels of phosphorus in the water column.
Results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program also suggest "partial support" of the Class A1 uses of Red Rock Reservoir. Using the median values from this survey from 2004 through 2008 (approximately 26 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus are 65, 52, and 77, respectively. According to Carlson (1977), the index value for total phosphorus places this reservoir in the hypereutrophic category; the index value for chlorophyll a places this reservoir in the eutrophic category, and the value for Secchi depth places this reservoir in between the eutrophic and hypereutrophic categories. These values suggest low levels of chlorophyll a and suspended algae in the water, poor water transparency, and extremely high levels of phosphorus in the water column.
The level of inorganic suspended solids is high at this lake and suggests that non-algal turbidity may cause water quality problems. The median inorganic suspended solids concentration at Red Rock Reservoir was 6.5 mg/L, which was the 37th highest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a very small population of cyanobacteria exists at Red Rock Reservoir, which does not suggest impairment at this lake. These data show that cyanobacteria comprised only 10% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (0.9 mg/L) was the 5th lowest of the 132 lakes sampled. Results of ISU/ACOE monitoring, however, do suggest that blooms of cyanobacteria occasionally occur at Red Rock Lake. According to the ISU/ACOE annual monitoring reports (e.g., Lutz and Esser 2002, Lutz and Cummings 2003, Lutz 2004, Lutz et al. 2005, and Lutz et al. 2006), blooms of cyanobacteria typically occur during July and August, especially under elevated pool conditions. These reports contain a summary of when these blooms have occurred at Red Rock Lake since 1990. The occurrence of cyanobacteria blooms in July 2002, June 29, 2004, and July 6, 2004 suggests a threat to the full support of Class A uses at this reservoir (no algal blooms were observed at this reservoir in 2003).
The Class B(WW-1) (aquatic life) uses of Red Rock Reservoir are assessed as "fully supported." None of the 53 samples collected during the 2006-2008 period as part of ISU/ACOE monitoring violated Class B(WW-1) criteria for pH or ammonia. Two of the 53 samples violated the Class B(WW-1) criterion for dissolved oxygen (4%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(WW-1) uses at Red Rock Reservoir.
The ISU and UHL lake survey data from 2004 through 2008 also show good chemical water quality at this lake. Results of this monitoring show no violations of the Class B(WW-1) criterion for ammonia in 25 samples and no violations of the Class A1,B(WW-1) criteria for pH in 26 samples. Three of 26 samples exceeded the Class B(WW-1) criterion for dissolved oxygen (12%). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(WW-1) uses of Red Rock Lake.
Information from the IDNR Fisheries Bureau suggests that the Class B(WW-1) uses are “fully supported,” however, sediment and nutrient loading to this lake and a large population of common carp remain concerns at this lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of ACOE/ISU fish contaminant monitoring at Red Rock Lake in 2006, 2007, and 2008. The composite samples of whole-fish common carp had low levels of contaminants (the ACOE/ISU samples are not analyzed for mercury or PCBs). Levels of total chlordane in the composite samples were as follows: 2006: 1.52 ppb; 2007: 0.14 ppb; 2008: 7.6 ppb. None of these levels approach the advisory trigger level of 600 ppb for chlordane. 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 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.
