Indian Lake IA 04-LDM-1007

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Indian Lake are assessed (monitored) as "not supported" due to aesthetically objectionable conditions caused by nuisance algae blooms that cause poor water transparency 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 70, 64, and 75 respectively for Indian Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Indian 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 extremely high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 15 samples. While the trophic state index value for chlorophyll a for the 2016 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.  

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 2016 assessment/listing cycle (algal growth, pH, and cyanobacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).  

The level of inorganic suspended solids was moderately high at Indian Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Indian Lake (3.3 mg/L) was ranked 75th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderately large population of cyanobacteria exists at Indian Lake. These data show that cyanobacteria comprised 90% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (33.6 mg/L) was ranked 100th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to exotic invasive species based on information from IDNR’s Fisheries Bureau and results from the ISU lake survey.   Information from the IDNR Fisheries Bureau shows that due to the crest elevation of the lake it is susceptible to flooding during extreme flooding events. This occurred in 1993, 2008, and 2010. As a result, common carp, bighead, and silver carp are present in this lake. 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 lake survey data from 2010-2014, however, show there were no violations of the criterion for ammonia in 15 samples(0%), one violation of the criterion for dissolved oxygen in 15 samples(7%), 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 Indian Lake.

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

Note: Gizzard shad were removed in 2014 through a low concentration of rotenone.