Windmill Lake IA 05-PLA-1482
Taylor County S36T69NR35W 4 mi E of New Market.
- 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
- 5/9/2019 8:43:07 AM
- Updated
- 5/17/2019 11:13:51 AM
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 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.
For the 2018 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 2012-2016 (approximately 20 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 68, and 70 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 very high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 20 samples. NOTE: A TMDL for impairments at Windmill Lakedue to algae and Turbidity was prepared by Iowa DNR and approved by the U.S. EPA in 2018. Thus, the impairments of Class A1 uses due to algae and turbidity are moved from IR Category 5a (impaired and TMDL required) to IR Category 4a (impaired; TMDL not required). The level of inorganic suspended solids was extremely 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 (19.6 mg/L) was ranked 133rd 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 Windmill Lake. These data show that cyanobacteria comprised 69% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.6 mg/L) was ranked 77th 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 20 samples(0%), one violation of the criterion for dissolved oxygen in 20 samples(5%), and no violations of the criterion for pH in 20 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 Windmill Lake. According to the DNR 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.