Blue Lake IA 06-WEM-1728
Alternate name(s) for this segment: Lewis and Clark Lake
Monona County S35T84NR46W 2 mi. W of Onawa.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 10/12/2018 3:14:47 PM
- Updated
- 3/6/2019 2:16:53 PM
The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water transparency and aesthetically objectionable conditions caused by algae blooms. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” (IR 3b) based on information from the DNR Fisheries Bureau. Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2014 through 2016, (2) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), and (3) information from the IDNR Fisheries Bureau.
Results of DNR beach monitoring from 2014 through 2016 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 2014 (16 samples), 2015 (17 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 Blue Lake Beach, the geometric means from 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 74 E. coli orgs/100 ml in 2014, 13 E. coli orgs/100 ml in 2015 and 19 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 19% in 2014, 6% 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 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 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 64, and 69 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 moderately 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.Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, Blue 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, Blue Lake will remain listed as "not supported" for the 2018 assessment/listing cycle. The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." 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 no violations of the criterion for pH in 15 samples(0%). Based on DNR'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.
Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Blue Lake. These data show that cyanobacteria comprised 56% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.3 mg/L) was ranked 78th of the 138 lakes sampled.
Note: A TMDL for the algae and turbidity impairments at Blue Lake was prepared by DNR 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.