Nine Eagles Lake IA 05-GRA-1361
Decatur County S18T67NR25W 3.5 mi. SE of Davis City.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Mesotrophic
- Trend
- Improving
- Created
- 10/16/2018 9:37:02 AM
- Updated
- 6/6/2019 2:10:11 PM
The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 5a) due to levels of indicator bacteria that exceed state water quality standards. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” (IR 2a). Fish consumption uses remain assessed (monitored) as “partially supported” (IR 5a) due to the existence of a fish consumption advisory. The Class C (drinking water) uses remain “not assessed” (IR 3a) due to a lack of information upon which to base an assessment. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2014 through 2016, (2) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) results from the EPA/IDNR fish tissue monitoring program in 2007, 2009, and 2015.
Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Nine Eagles Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (32 samples), 2015 (16 samples) and 2016 (15 samples), as part of the DNR beach monitoring program. According to DNR’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). Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring at Nine Eagles Lake in 2007, 2009, and 2015. 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. Sampling conducted in 2007 and 2009 also showed that the levels of mercury in largemouth bass (0.412 ppm and 0.534 ppm, respectively) were above the one meal per week consumption advisory. Additionally, follow up sampling in 2015showed that the levels of mercury in largemouth bass (0.498 ppm) was also above the one meal per week consumption advisory.Therefore the consumption advisory remains at this lake and the fish consumption uses remain assessed as "partially supported."