Three Mile Lake IA 05-GRA-1371
Union County S32 T73N R29W approximately 3 miles N or Afton.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 1 - All designated uses are met.
- Trophic
- Eutrophic
- Trend
- Improving
- Created
- 5/8/2019 8:41:33 AM
- Updated
- 5/9/2019 8:31:13 AM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2014 | Class BLW | Organic Enrichment: Low Dissolved Oxygen | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” [Note: this lake is not designated for Class A1 (primary contact recreation) uses in the Iowa Water Quality Standards.] The Class C (drinking water) uses are assessed (monitored) as "fully supported" (IR 2a) primarily based on results of Syngenta-sponsored monitoring. Fish consumption uses remain assessed (monitored) as “fully supported” (IR 2a) based on results of fish contaminant monitoring in 2010. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, (3) results of Syngenta-sponsored monitoring for atrazine from 2010 through 2012, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2010 and 2011.
Using the median values from these surveys from 2012-2016 (approximately 14 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 60, 62, and 55 respectively for Three Mile Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Three Mile 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 relatively low levels of phosphorus in the water column. The level of inorganic suspended solids was moderately high at Three Mile Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Three Mile Lake (3.55 mg/L) was ranked 79th 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 Three Mile Lake. These data show that cyanobacteria comprised 91% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.5 mg/L) was ranked 74th of the 138 lakes sampled. 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 14 samples(0%), 3 violations of the criterion for dissolved oxygen in 14 samples(21%), and no violations of the criterion for pH in 14 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 Three Mile Lake. Three Mile Lake was assessed as "partially supported" for the 2014 assessment/listing cycle. Based on DNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on Dissolved Oxygen. 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 Dissolved Oxygenis suggested for delisting for the 2018 assessment/listing cycle.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring at Threemile Lake in 2010.The composite samples of fillets from channel catfish had low levels of contaminants.Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.189 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.Levels of mercury in the composite sample of walleye fillets (0.653 ppm), however, exceeded the advisory trigger level.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.Based onDNR/IDPH protocol, two samples with mercury levels greater than the advisory level are necessary to suggest the issuance of a fish consumption advisory.The fish contaminant data generated from the 2010 RAFT sampling suggest that mercury levels are high and justify follow-up sampling at this lake to determine if an advisory is justified.Follow-up sampling was conducted in 2011 and suggests "full support" of fish consumption uses at Threemile Lake.The composite samples of fillets from channel catfish had low levels of walleye fillets were as follows: mercury: 0.120 ppm, which is below the advisory threshold.