Red Rock Reservoir IA 04-LDM-1017

Results of ACOE beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria were measured at multiple beaches located at Red Rock Reservoir as part of the ACOE beach monitoring program. North Overlook Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (21 samples), 2013 (20 samples) and 2014 (19 samples), as part of the ACOE beach monitoring program. Whitebreast Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (21 samples), 2013 (16 samples) and 2014 (15 samples), as part of the ACOE beach monitoring program. High water levels at Red Rock Reservoir during the 2013 and 2014 sampling seasons led to flooding and closures of the beaches. Beaches were not sampled during flooded conditions. 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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 North Overlook Beach, the geometric means from 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml. The geometric mean from 2012, however, was greater than the Iowa water quality standard of 126 E.  coli orgs/100ml and therefore suggests impairment of the Class A1 uses.   The geometric mean was 137 E.  coli orgs/100 ml in 2012, 102 E.  coli orgs/100 ml in 2013 and 98 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 52% in 2012, 35% in 2013 and 32% in 2014.   The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2012, 2013 and 2014.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

At Whitebreast Beach, the geometric means from 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 70 E.  coli orgs/100 ml in 2012, 20 E.  coli orgs/100 ml in 2013 and 39 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 33% in 2012, 13% in 2013 and 7% in 2014.   The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2012.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

Results of water quality monitoring at the ISU/ACOE long-term station on the main reservoir near the dam and ISU surveys suggest that the Class A1 uses should be assessed (monitored) as "partially supported."  Using the median values from these surveys from 2010-2014, Carlson’s (1977) trophic state indices for Secchi depth (67 samples), chlorophyll a (74 samples), and total phosphorus (93 samples) were 67, 57, and 75 respectively for Red Rock Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Red Rock Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest relativley 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 data show no violations of the Class A1 criterion for pH in 93 samples.

The level of inorganic suspended solids was moderately high at Red Rock Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Red Rock Lake (5.66 mg/L) was ranked 92nd among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a small population of cyanobacteria exists at Red Rock Lake. These data show that cyanobacteria comprised 88% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (9.7 mg/L) was ranked 27th of the 138 lakes sampled.

The Class B(WW-1) (aquatic life) uses are assessed (monitored) as "fully supported." The ISU/ACOE monitoring data from 2010 through 2014 show good chemical water quality at this lake.   Results of this monitoring show there were no violations of the criterion for ammonia in 92 samples(0%), 3 violations of the criterion for dissolved oxygen in 93 samples(3%), and no violations of the criterion for pH in 93 samples(0%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) 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 2012, 2013, and 2014.   The composite samples of whole-fish common carp had low levels of contaminants.   Levels of total chlordane in the composite samples were as follows: 2012: 0.003 ppm; 2013: 0.003 ppm; 2014: 0.130 ppm.   None of these levels approach the advisory trigger level of 0.6 ppm for chlordane. In 2012, 2013, and 2014, composite samples of whole-fish carp were analyzed for total PCBs and Aroclors 1248, 1254, and 1260. Total PCBs in composite samples of whole-fish carp were 0.002 ppm (2012) and 0.002 (2013). PCB Aroclors 1248, 1254, and 1260 were all 0.0002 ppm (2014). 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.