Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by nuisance algae blooms that cause poor water transparency. The Class B(LW) (aquatic life) uses are assessed (evaluated) as "partially supported" due to concern over fish kills and the introduction of gizzard shad and silver carp at this lake. Fish consumption uses remain “not assessed” due to a 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 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
Note: A TMDL for organic enrichment and noxious aquatic plants (cyanobacteria) at Indian Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2008, 2010, 2012, and 2014 assessment/listing cycle (algal growth, pH, and cyanobacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2014 reporting cycle, the Class A1 (primary contact recreation) uses for Indian Lake are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by algal and non-algal turbidity. Using the median values from the ISU and UHL lake surveys from 2008-2012(approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 69, 63, and 75 respectively for Indian Lake. According to Carlson (1977) the Secchi depth and chlorophyll a index values place Indian Lake in between the eutrophic and hypereutrophic categories, while the total phosphorus value places this lake in the hypereutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and extremely high levels of phosphorus in the water column. Indian Lake was listed as "not supporting" its Class A1 uses in the 2012 Assessment/listing cycle due to aesthetically objectionable conditions caused by high levels of algae (Chlorophyll a index value = 70). While the trophic state index value for chlorophyll a for the 2014 IR cycle is below the impariment trigger of 65, IDNR's methodology requires 2 consecutive assessment/listing cycles with trophic state index values of 63 or less to propose delisting. Therefore, the Class A1 uses remain listed as "not supporting." In addition, the chlorophyll a index value suggests "partial support" of the designated uses.
The levels of inorganic suspended solids at this lake were moderately high and may contribute to the impairment at this lake. The median level of inorganic suspended solids in Indian Lake (3.8 mg/L) and ranked 68th of the 134 lakes sampled by the ISU and UHL programs.
Data from the 2008-2012 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Indian Lake, which likley contributes to impairment at this lake. These data show that cyanobacteria comprised 100% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (16.7 mg/L) was also the 30th highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from IDNR’s Fisheries Bureau and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau shows that gizzard shad and silver carp were introduced to this lake during the 2008 flooding. Fish kills also remain a concern at this lake. These potential impairments are not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but are appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation. The ISU and UHL lake surveys data from 2008-2012, however, show no violations of the Class B(LW) criteria for ammonia in 15 samples, no violations for pH in 15, and only one violation of the Class B(LW) criterion for dissolved oxygen in 15 samples (7%). Based on IDNR's assessment methodology, the single violation is not significantly greater than 10% of the samples and therefore does not constitute an impairment of the Class B(LW) uses.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
