Lake Hendricks IA 01-WPS-356

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Hendricks are assessed (monitored) as "not supported" due to poor water transparency, 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 69, and 71 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 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 37th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderate population of cyanobacteria exists at Lake Hendricks. These data show that cyanobacteria comprised 85% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (20.2 mg/L) was ranked 66th of the 138 lakes sampled.

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 2010-2014 show there were one violation of the criterion for ammonia in 15 samples(7%), 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 IDNR'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/IDNR 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.