Lake Hendricks IA 01-WPS-356

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Hendricks are assessed (monitored) as "not supported" due to aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 71, and 72 respectively for Lake Hendricks. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Hendricks in between the Eutrophic and the Hypereutrophic categories. These values suggest very 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 8 violations of the Class A1 criterion for pH in 15 samples (53%).

The level of inorganic suspended solids was relatively low at Lake Hendricks, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Lake Hendricks (2.33 mg/L) was ranked 51st among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a large population of cyanobacteria exists at Lake Hendricks, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 84% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (45.6 mg/L) was ranked 118th 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 2012-2016. 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 (monitored) as "not supported" due to violations of the Class A1,B(LW) criterion for pH. Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and 8 violations of the criterion for pH in 15 samples(53%). Based on DNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Lake Hendricks.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR turtle contaminant (RAFT) monitoring at Lake Hendricks in 2010. The composite samples of shoulder tissue from snapping turtle had low levels of contaminants.Levels of primary contaminants in the composite sample of snapping turtle shoulder were as follows: mercury: 0.132 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. 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 turtle contaminant data generated from the 2010 RAFT sampling conducted at this lake show that 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.