Blue Lake IA 06-WEM-1728

Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Blue Lake Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (15 samples), 2013 (15 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 Blue Lake 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 43 E.  coli orgs/100 ml in 2012, 30 E.  coli orgs/100 ml in 2013 and 74 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 13% in 2012, 7% in 2013 and 19% in 2014.   None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses.

For the 2016 assessment/listing cycle, however, the Class A1 (primary contact recreation) uses of Blue 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 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 69, 65, and 68 respectively for Blue Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Blue 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 no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was very high at Blue Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Blue Lake (13.2 mg/L) was ranked 126th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderately large population of cyanobacteria exists at Blue Lake. These data show that cyanobacteria comprised 80% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (30.3 mg/L) was ranked 94th 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.   Information from the IDNR Fisheries Bureau suggests that Blue Lake has a poor recreational fishery and a large carp population.   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 Blue Lake.

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.

Note:  A TMDL for the algae and turbidity impairments at Blue Lake was prepared by IDNR and approved by EPA in January 2009.   Because the 2009 TMDL includes all of the impairments identified for the current (2016) assessment/listing cycle, this lake will remain in IR Category 4a (impaired; TMDL approved) for the 2016 cycle.