Prairie Rose Lake IA 05-NSH-1462

Results of IDNR beach monitoring from 2013 through 2014 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Prairie Rose Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2013 (12 samples) and 2014 (16 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 Prairie Rose Beach, the geometric means from 2013 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml. The geometric mean from 2014, 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 78 E.  coli orgs/100 ml in 2013 and 215 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 25% in 2013 and 50% 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, the Class A1 (primary contact recreation) uses of Prairie Rose Lake are assessed (monitored) as "partially supported" due to poor water transparency and aesthetically objectionable conditions caused by algae blooms based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 10 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 65, and 68 respectively for Prairie Rose Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Prairie Rose Lake in the Eutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 10 samples.

The level of inorganic suspended solids was relatively low at Prairie Rose Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Prairie Rose Lake (2.5 mg/L) was ranked 39th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a large population of cyanobacteria exists at Prairie Rose Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 96% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (38.8 mg/L) was ranked 110th of the 138 lakes sampled. This median is in the worst 25% of the 138 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa's narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2010-2014. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. Assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.

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 10 samples(0%), no violations of the criterion for dissolved oxygen in 10 samples(0%), and one violation of the criterion for pH in 10 samples(10%). 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 Prairie Rose 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 relatively low at this lake (maximum value = 3 mg/l; median = 0.3 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at Prairie Rose Lake in 2003 and 2007.   The composite samples of fillets from channel catfish and largemouth bass had very low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: <0.0181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   Follow up sampling in 2007 also showed low levels of primary contaminants.   Data from 2007 show the composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants.    Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0273 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.091 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 fish contaminant data generated from the 2003 and 2007 RAFT sampling conducted at Prairie Rose Lake show that 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.

Note: Prairie Rose Lake was drawn down in in July of 2011 and refilled in September of 2012 for restoration purposes.  As a result, no samples were collected during that time. While the lake was drawn down, Stabilization of the eroding shoreline and removal of 60,000 cubic yards of sediment was completed and undesirable fish species (e.g. common carp)were removed from the lake and watershed. The lake was restocked starting in April of 2013. In lake dredging started in mid-July. Approximately 185,000 CY of sediment were to be removed from Prairie Rose Lake. The project was completed in 2015. This assessment does not include post restoration data.