White Oak Conservation Area Lake IA 03-SSK-929

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of White Oak 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 68, 66, and 73 respectively for White Oak Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place White Oak Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest high 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 one violation of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was moderately high at White Oak Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in White Oak Lake (6.33 mg/L) was ranked 101st among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a large population of cyanobacteria exists at White Oak Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 86% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (44.2 mg/L) was ranked 116th of the 138 lakes sampled. This median is in the worst 25% of the 138 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa's narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2010-2014. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. Assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to nuisance algae (cyanobacteria). Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), 2 violations of the criterion for dissolved oxygen in 15 samples(13%), and one violation of the criterion for pH in 15 samples(7%). 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 White Oak Lake.

High levels of algae and turbidity at this lake remain a concern for support of aquatic life uses and represent a potential impairment of the Class B(LW) aquatic life uses.   This potential impairment, however, is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.