Brushy Creek Lake IA 04-UDM-1276

Results of IDNR beach monitoring from 2012 through 2013 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Brushy Creek Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (15 samples) and 2013 (17 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 Brushy Creek Beach, the geometric means from 2012 and 2013 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 18 E.  coli orgs/100 ml in 2012 and 98 E.  coli orgs/100 ml in 2013.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 7% in 2012 and 24% in 2013.   The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2013.   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 Brushy Creek 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 53, 56, and 61 respectively for Brushy Creek Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Brushy Creek Lake in the Eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very good water transparency, and moderately high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was extremely low at Brushy Creek Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Brushy Creek Lake (1.6 mg/L) was ranked 2nd 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 Brushy Creek Lake. These data show that cyanobacteria comprised 73% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (6.7 mg/L) was ranked 19th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau and results from the ISU lake surveys. Information from the IDNR Fisheries Bureau indicate this lake has excessive growth of curly leaf pondweed and brittle naiad. Additionally Zebra mussel veligers were recently discovered in the lake. While the lake shows good water quality now, the potential of poor water quality in the future is possible. 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 one violation of the criterion for pH in 15 samples(7%). 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 Brushy Creek Lake.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.   EPA/IDNR fish contaminant (RAFT) monitoring at Brushy Creek Lake in 2013.    The composite samples of fillets from largemouth bass and catfish had low levels of contaminants.    Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.232 ppm.    Levels of primary contaminants in the composite sample of catfish fillets were as follows: total PCBs: <0.6 ppm; and technical chlordane: <0.2 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 YEAR RAFT sampling conducted at this Brushy Creek 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.