Big Hollow Lake IA 02-ICD-6496

Results of DNR beach monitoring from 2015 through 2016 suggest that the Class A1 uses are (Evaluated) "Fully Supported." Levels of indicator bacteria at Big Hollow Recreation Area Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2015 (15 samples) and 2016 (15 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) 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 Big Hollow Recreation Area Beach, the geometric means from 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 27 E. coli orgs/100 ml in 2015 and 11 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2015 and 0% in 2016. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Big Hollow Lake are assessed (monitored) as "not supported" due to aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH 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 62, 64, and 68 respectively for Big Hollow Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Big Hollow Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and high levels of phosphorus in the water column. The data show 4 violations of the Class A1 criterion for pH in 15 samples (27%). Although the index value for chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Big Hollow Lakewas 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, Big Hollow Lakewill remain listed as "not supported" for the 2018 assessment/listing cycle.

The level of inorganic suspended solids was low at Big Hollow Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Big Hollow Lake (1.6 mg/L) was ranked 9th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Big Hollow Lake. These data show that cyanobacteria comprised 88% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (26.7 mg/L) was ranked 89th 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 pH. Information from the DNR Fisheries Bureau suggests problems at this lake are likely due to the numerous flooded timber areas on this lake as a result of its construction. Decomposition of timber, brush, and other terrestrials plants have released an abundance of nutrients that caused massive algal and duckweed blooms. Additionally, decomposition can lead to pH problems. Fisheries biologists have reported that submergent vegetation has slowly begun to establish and expect water quality to improve in the future. Results of the ISU lake survey from 2012-2016 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 4 violations of the criterion for pH in 15 samples(27%). 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 Big Hollow Lake.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR fish contaminant (RAFT) monitoring at Big Hollow Lake in 2012 and 2015. The sample of shoulder muscle from Snapping Turtle had low levels of contaminants. Levels of primary contaminants in the 2012 sample of Snapping Turtle shoulder muscle was mercury: 0.329 ppm. in 2012 and0.16 ppm in 2015. 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 2012 RAFT sampling conducted at this Big Hollow 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.