Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2006 through 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007 and 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due violations of the state water quality standard for indicator bacteria. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” The Class C (drinking water) uses are “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses are assessed (monitored) as “partially supported” due to the issuance of a fish consumption advisory at this lake. Sources of data for this assessment include: (1) results of the IDNR-UHL beach monitoring program from 2006 through 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007 and 2008.
EXPLANATION: Results of IDNR beach monitoring from 2006 through 2008 suggest that the Class A1 uses are "fully supported." Levels of indicator bacteria at Red Haw Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (16 samples), 2007 (15 samples), and 2008 (15 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. 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”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Red Haw Lake beach, the geometric means of all 34 thirty-day periods during the summer recreation seasons of 2006, 2007, and 2008 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. These results suggest generally low levels of bacteria. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 6% in 2006, 13% in 2007 and 13% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest "full support" of the Class A1 (primary contact recreation) uses. However, Red Haw Lake was listed on the 2008 impaired waters list due to 1 violation of the geometric mean standard in 2004. Based on IDNR's assessment methodology two consecutive assessment/listing cycles with no violations of the geometric mean standard are necessary to propose de-listing of a bacteria impairment. Therefore, Red Hawk Lake continues to be assessed as impaired for bacteria.
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Red Haw Lake are “fully supported.” Using the median values from these surveys from 2004 through 2008 (approximately 29 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 52, 53, and 56 respectively for Red Haw Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Red Haw Lake in the eutrophic category. These values suggest low levels of chlorophyll a and suspended algae in the water, very good water transparency, and relatively low levels of phosphorus in the water column. NOTE: A fishery renovation was completed in 2002, which has led to improved water clarity at Red Haw Lake.
The level of inorganic suspended solids is low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Red Haw Lake was 1.0 mg/L, which was the 6th lowest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a very small population of cyanobacteria exists at Red Haw Lake, which does not suggest impairment at this lake. These data show that cyanobacteria comprised 74% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (3.7 mg/L) was the 20th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau, and results from the ISU and UHL lake surveys. The ISU and UHL lake surveys show that from 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 29 samples, one violation of the Class B(LW) criterion for dissolved oxygen in 29 samples (3%), and no violations of the Class A1,B(LW) criterion for pH in 29 samples. Based on IDNR’s assessment methodology the violation of the dissolved oxygen criterion is not significantly greater than 10% of the samples and therefore does not suggest impairment of the Class B(LW) uses of Red Haw Lake.
The Class C (drinking water) uses remain "not assessed" due to lack of water quality information on which to base such an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2004-08 show that nitrate levels are very low at this lake (maximum value = 0.4 mg/l; median = 0.05 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Red Haw Lake in 2007 and 2008. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2007 RAFT sampling conducted at Red Haw Lake show that levels of mercury are sufficiently high for concern and thus justify follow-up monitoring. Results from the 2007 sampling show that the level of mercury in the sample of largemouth bass fillets (0.516 ppm) exceeds the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow-up sampling conducted in 2008 showed that levels of mercury in largemouth bass (0.428 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm). Thus a one meal per week fish consumption advisory was issued for Red Haw Lake and the fish consumption uses are assessed as “not supported.”
