Saylorville Reservoir IA 04-UDM-1213
Polk County Saylorville Dam to Polk-Dallas county line.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 5/10/2019 9:20:16 AM
- Updated
- 8/29/2019 9:22:44 AM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2006 | Class A1 | Bacteria: Indicator Bacteria- E. coli | Ambient monitoring: Corps of Engineers/Iowa DNR-Lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 (primary contact recreation) uses of Saylorville Reservoir are assessed (monitored) as "not supported” due to poor water transparency caused by non-algal turbidity. The Class B(WW-1) (aquatic life) uses are assessed (monitored) as "fully supported." Fish consumption uses were assessed (monitored) as "fully supported" based on ACOE-sponsored annual fish contaminant monitoring from 2012-14. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012-2016 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted from 2012-2016 by Iowa State University as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
Results of ACOE beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria were measured at multiple beaches located at Saylorville Reservoir as part of the ACOE beach monitoring program. Oak Grove Beach was monitored once per week during the primary contact recreation seasons (May through September) of 2014 (6 samples), 2015 (12 samples) and 2016 (17 samples), as part of the ACOE beach monitoring program.Sandpiper Beach was monitored once per week during the primary contact recreation seasons (May through September) of 2014 (8 samples), 2015 (14 samples) and 2016 (17 samples), as part of the ACOE 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 Oak Grove 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 14 E. coli orgs/100 ml in 2014, 24 E. coli orgs/100 ml in 2015 and 12 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 0% in 2014, 8% in 2015 and 6% 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. At Sandpiper 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 41 E. coli orgs/100 ml in 2014, 38 E. coli orgs/100 ml in 2015 and 17 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 25% in 2014, 21% in 2015 and 6% 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. Saylorville Reservoir was assessed as "not supported" for the 2006 assessment/listing cycle. Based on DNR’s assessment methodology 2 consecutive assessment/listing cycles without violations of the geometric mean criterion and without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on bacteria violations. There were no violations of the geometric mean criterion and there were less than 10% of the samples exceeding the single-sample maximum criterion for the 2016 or current 2018 assessment listing cycle. Therefore, the impairment for indicator bacteria is suggested for delisting for the 2018 assessment/listing cycle. For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Saylorville Lake are assessed (monitored) as "partially supported" due to poor water transparency based on information from the ISU lake survey and ISU/ACOE long-term station on the main reservoir near the dam. Using the median values from the ISU lake survey from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 58, and 72 respectively for Saylorville Lake.Additionally, using the median values from theISU/ACOE long-term stationfrom 2012-2016 (approximately 85 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 60, and 87 respectively.According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Saylorville Lake in between the Eutrophic and the Hypereutrophic categories.These values suggest relatively low levels of chlorophyll a and suspended algae in the water, poor water transparency, and very high levels of phosphorus in the water column.The data show no violations of the Class A1 criterion for pH in 15 samplesbased on information from the ISU lake survey andshow no violations of the Class A1 criterion for pH in 85 samples from theISU/ACOE long-term station. The level of inorganic suspended solids was relatively low at Saylorville Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Saylorville Lake (8.6 mg/L) was ranked 115th among the 138 lakes by the ISU lake survey. Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at Saylorville Lake. These data show that cyanobacteria comprised 65% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (8.2 mg/L) was ranked 42nd of the 138 lakes sampled. The Class B(WW-1) (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%), one violation of the criterion for dissolved oxygen in 15 samples(7%), and no violations of the criterion for pH in 15 samples(0%). Additionally,Results of the ISU/ACOE long-term stationfrom 2012-2016 show there were no violations of the criterion for ammonia in 85 samples(0%), 4 violations of the criterion for dissolved oxygen in 84 samples(5%), and no violations of the criterion for pH in 85 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(WW-1) uses of Saylorville Lake.
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 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.