Viking Lake IA 05-NOD-1407
Montgomery County S6T71NR36W 4 mi. E of Stanton.
The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria. The Class B(LW) aquatic life uses are assessed (monitored) as “fully supported.” The Class C (drinking water) uses remain “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2012 through 2014, (2) results of the statewide survey of Iowa lakes conducted from 2010 through 2014 by Iowa State University (ISU), and (3) information from the IDNR Fisheries Bureau. Note: this lake was drained and its fishery was renovated by IDNR in 2006, and watershed improvements were also made (e.g., installation of silt-retention structures). Positive changes in water quality may result from this renovation which will affect future assessments.
Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Viking 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 Viking 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 17 E. coli orgs/100 ml in 2012, 62 E. coli orgs/100 ml in 2013 and 19 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, 33% in 2013 and 6% in 2014. 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. However, for the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Viking 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 62, 62, and 61 respectively for Viking Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Viking 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 moderately 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 low at Viking Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Viking Lake (2 mg/L) was ranked 10th 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 Viking Lake. These data show that cyanobacteria comprised 93% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (24.6 mg/L) was ranked 77th of the 138 lakes sampled. NOTE: Extensive in-lake and watershed restoration work was completed at Viking Lake between 2000-2006, with over 10 detention basins being built in the watershd to reduce nutrient and sediment loads to the lake. Water quality improvements at Viking Lake can be attributed to these efforts. 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 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 Viking 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 extremely low at this lake (maximum value = 0.2 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.