Windmill Lake IA 05-PLA-1482
Taylor County S36T69NR35W 4 mi E of New Market.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 6/14/2016 3:41:23 PM
- Updated
- 12/19/2016 11:25:00 AM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2012 | Class BLW | Organic Enrichment: Low Dissolved Oxygen | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water transparency caused by algae blooms and non-algal turbidity that violates Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The Class B(LW) aquatic life uses are assessed (monitored) as “fully supported." 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 the statewide survey of Iowa lakes conducted from 2010 through 2014 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.
For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Windmill Lake are assessed (monitored) as "not 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 68, and 69 respectively for Windmill Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Windmill Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very 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. The level of inorganic suspended solids was very high at Windmill Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Windmill Lake (16.8 mg/L) was ranked 130th 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 Windmill Lake. These data show that cyanobacteria comprised 95% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (33.9 mg/L) was ranked 102nd 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 2010-2014 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%). 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 Windmill Lake. Windmill Lake was assessed as "partially supported" due to organic enrichment/low DO for the 2012 assessment/listing cycle. Based on IDNR’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 violations. There were less than 10% of the samples exceeding the single-sample maximum criterion for both the 2014 and 2016 assessment/listing cycles. Therefore, the impairment (5a) for dissolved oxygen is suggested for delisting for the 2016 assessment/listing cycle. Note: this IR Category 5a impairment for organic enrichment/low DO appears to have been inadvertently omitted from Iowa's 2012 and 2014 Section 303(d) lists. According to the IDNR Fisheries Bureau, both grass carp and common carp likely contribute to poor water clarity at this lake. The population of common carp, however, is relatively small, and thus is believed to have a relatively minor impact on this lake's water quality. Nutrient loading to the water column and non-algal turbidity remain water quality concerns at this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.