Nine Eagles Lake IA 05-GRA-1361

Results of IDNR beach monitoring from 2012 through 2014 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 2012 (15 samples), 2013 (27 samples) and 2014 (32 samples), as part of the IDNR beach 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) 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 Nine Eagles 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 11 E.  coli orgs/100 ml in 2012, 14 E.  coli orgs/100 ml in 2013 and 54 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 0% in 2012, 15% in 2013 and 31% in 2014.   The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2014.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

For the 2016 assessment/listing cycle, however, the Class A1 (primary contact recreation) uses of Nine Eagles Lake are assessed (monitored) as "fully supported" based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 49, 44, and 46 respectively for Nine Eagles Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Nine Eagles Lake in the Mesotrophic category. These values suggest extremely low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and extremely low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

Note:  A TMDL for turbidity at Nine Eagles Lake was prepared by IDNR and approved by EPA in 2001.   Through implementation of this TMDL, water clarity at this lake had improved such that the lake was de-listed for the 2004 assessment/listing cycle.    Because, however, the 2006, 2008, 2010, 2012, 2014, and 2016 Section 303(d) impairments due to indicator bacteria and mercury in fish tissue at Nine Eagles Lake were not addressed in the TMDL, this waterbody remains in Category 5a (impaired; TMDL required) for the 2016 cycle.

The level of inorganic suspended solids was low at Nine Eagles Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Nine Eagles Lake (2 mg/L) was ranked 10th 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 Nine Eagles Lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (8.1 mg/L) was ranked 23rd of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 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(LW) uses of Nine Eagles Lake.

The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU surveys from 2010-2014 show that nitrate levels are extremely low at this lake (maximum value = 0.2 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.

Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at Nine Eagles Lake in 2001, 2005, 2007, and 2009.   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 level of mercury in the samples of largemouth bass in 2001 (0.26 ppm) exceeded the IDNR/IDPH interim trigger level of 0.20 ppm for a one meal per week consumption advisory.   The level of mercury in the 2001 sample was well below the “do not eat” trigger level for mercury of 1.0 ppm.   According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified.   Because the level of mercury in sample of largemouth bass fillets from a 2005 follow-up sampling (0.30 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory was justified.   This advisory was issued by IDNR and IDPH in January 2006.   [Note:  the advisory threshold for a 1 meal/week consumption advisory was changed form 0.2 ppm to 0.3 ppm in 2007 to be consistent with U.S.  EPA's recommendation for a tissue-based water quality criterion for mercury.]  According to IDNR’s assessment methodology, the existence of a one meal/week consumption advisory indicates that fish consumption uses should be assessed as “partially supported.”  Follow up 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.   Therefore the consumption advisory remains at this lake and the fish consumption uses remain assessed as "partially supported."