Indian Lake IA 04-LDM-1007

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Indian Lake are assessed (monitored) as "not 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 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 72, and 74 respectively for Indian Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Indian Lake in the Hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and very high levels of phosphorus in the water column. The data show 2 violations of the Class A1 criterion for pH in 15 samples (13%).

Note:A TMDL for organic enrichment and noxious aquatic plants (cyanobacteria) at Indian Lake was prepared by DNR and approved by EPA in 2005.Because all Section 303(d) impairments identified for the 2016assessment/listing cycle (algal growth, pH, and cyanobacteria) are addressed by the TMDL, thiswaterbodyis 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 (4.5 mg/L) was ranked 91st 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 Indian Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (44.2 mg/L) was ranked 117th 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 (evaluated) as “partially supported” due to exotic invasive species based on information from DNR’s Fisheries Bureau and results from the ISU lake survey. Information from the DNR 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 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 2 violations of the criterion for pH in 15 samples(13%). Based on DNR'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.