Assessment Comments
Assessment is based on results of (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 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 2008-2012 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 high levels of pathogens. Low water clarity also suggests an impairment at this lake due to aesthetically objectionable conditions. 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 2010-2012. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 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 2008-12 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
EXPLANATION: Results of ACOE beach monitoring at White Breast and North Overlook beaches from 2010 through 2012 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at White Breast beach were monitored approximately weekly during the primary contact recreation seasons (May through September) of 2010 (2 samples), 2011 (18 samples), and 2012 (22 samples) as part of the ACOE beach monitoring program. Only 2 samples were collected in 2010 due to high water at the beaches. 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 2014 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 Whitebreast beach, the geometric means from 2010, 2011, and 2012 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 5 E. coli orgs/100 ml in 2010 and 14 E. coli orgs/100 ml in 2011, and 116 E. coli orgs/100 ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 36% in 2010, 0% in 2011 and 55% in 2012. These results suggest that Class A1 uses add Red Rock Lake are "partially supported."
At North Overlook beach, the geometric mean from 2011 was below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 17 E. coli orgs/100 ml in 2011. The geometric mean in 2012, however, was above the water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 300 E. coli orgs/100 ml in 2011, and 116 E. coli orgs/100 ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2011 and 55% in 2012. These results suggest that Class A1 uses add Red Rock Lake are "not supported."
Results of water quality monitoring at the ISU/ACOE long-term station on the main reservoir near the dam and ISU and UHL surveys suggest that the Class A1 uses should be assessed (monitored) as "partially supported." Using the median values from these surveys from 2008-2012 (approximately 98 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus are 67, 54, and 91, 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 Secchi depth value places this reservoir in between the eutrophic and hypereutrophic categories. These values suggest relatively 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 moderately 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 7.0 mg/L, and ranked 94th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a small population of cyanobacteria exists at Red Rock Reservoir, which does not suggest impairment at this lake. These data show that cyanobacteria comprised 98% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (7.3 mg/L) and ranked 12th of the 134 lakes sampled. Results of ISU/ACOE monitoring also 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 ISU and UHL lake survey data and the ISU/ACOE monitoring data from 2008 through 2012 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 98 samples and no violations of the Class A1,B(WW-1) criteria for pH in 98 samples. 3 of 98 samples exceeded the Class B(WW-1) criterion for dissolved oxygen (3%). 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 2008, 2009, and 2010. The composite samples of whole-fish common carp had low levels of contaminants. Levels of total chlordane in the composite samples were as follows: 2008: 7.6 ppb; 2009: 3.0 ppb; 2010: 12.3 ppb. None of these levels approach the advisory trigger level of 600 ppb for chlordane. In addition, the 2009 and 2010 composite samples of whole-fish carp were analyzed for PCBs (Aroclors), and composite samples of fillets from a predator species (largemouth bass (Micropterus salmoides)) were analyzed for mercury. Levels of PCBs in composite whole-fish carp samples for all Aroclors analyzed (1016, 1221, 1232, 1242, 1248, 1254, and 1260) were all below levels of detection (range from 0.02 to 0.09 ppm). The average level of mercury in the composite sample of largemouth bass fillets in 2009 was 0.1 ppm and in 2010 was 0.12 ppm. The levels of PCBs and mercury seen in fish tissue samples from ISU/ACOE station 8 in Red Rock Reservoir are well below the one meal per week advisory trigger of 0.20 ppm for total PCBs (sum of Aroclors 1248, 1254, and 1260) and for mercury (0.30 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 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.
