Bob White Lake IA 05-CHA-1338

Results of DNR beach monitoring from 2000 through 2002 suggest that the Class A1 uses are assessed (evaluated) as "not supported" (this beach was not monitored for indicator bacteria during recreational seasons of 2003 through 2010 and 2012 through 2014). Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Levels of indicator bacteria at Bob White Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2000 (18 samples), 2001 (16 samples), and 2002 (29 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) all thirty-day geometric means for 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 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported”.Also, 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 3-35of U.S.EPA 1997b).

At Bob White Lake beach, the geometric means for 8 of the 12 thirty-day periods during the summer recreation season of 2011 exceeded the Iowa water quality standard of 126 E.coli orgs/100 ml; none of the geometric means exceeded this standard during the recreational seasons of 2000 (14 geometric means) or 2002 (25 geometric means). Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E.coli orgs/100 ml) was significantly greater than 10% in 2002 (4 of 18 samples, 22%). According to DNR’s assessment methodology and U.S.EPA guidelines, these results suggest impairment (“nonsupport”) of the Class A1 primary contact recreation uses due to geometric mean values that exceed Iowa’s Class A1 criterion.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Bob White Lake are assessed (monitored) as "not 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 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 83, 64, and 84 respectively for Bob White Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Bob White Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.Information from the DNR Fisheries Bureauindicatethat commoncarp werea problem in this lake. The fishery was renovated in September of 2015 and theexpectwater clarity to improve in coming years.Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Bob White Lake was listed as partially supporting its Class A1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Bob White Lake will remain listed as "not supported" for the 2018 assessment/listing cycle.

The level of inorganic suspended solids was extremely high at Bob White Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Bob White Lake (38.7 mg/L) was ranked 138th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a small population of cyanobacteria exists at Bob White Lake. These data show that cyanobacteria comprised 38% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (2.3 mg/L) was ranked 18th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "not supported" due to violations of the Class A1,B(LW) criterion for DO. Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), 4 violations of the criterion for dissolved oxygen in 15 samples(27%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Bob White 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 2012-2016 show that nitrate levels are relatively low at this lake (maximum value = 3.1 mg/l; median = 0.4 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.