Lower Gar Lake IA 06-LSR-1646

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lower Gar Lake are assessed (monitored) as "partially 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 66, and 68 respectively for Lower Gar Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lower Gar Lake in the Eutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

Note: A TMDL for turbidity at Lower Gar Lake was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle.    Because all Section 303(d) impairments identified for the 2016 assessment/listing cycle [turbidity (algal and inorganic)] are addressed by the TMDL, this waterbody remains in IR Category 4a.  

The level of inorganic suspended solids was high at Lower Gar Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Lower Gar Lake (8.4 mg/L) was ranked 108th 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 Lower Gar Lake. These data show that cyanobacteria comprised 67% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.3 mg/L) was ranked 58th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to high levels of (inorganic) turbidity related primarily to sediment re-suspension at this shallow lake and due to an invasive species introduction of Zebra Mussels.  This lake was infested with Zebra mussels in 2012 and the population exploded in 2015. This invasive species will likely cause water quality to degrade in the future. This potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation. Results of the ISU lake survey from 2010-2014 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 no violations of the criterion for pH in 15 samples(0%). 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 Lower Gar Lake.

Fish consumption uses were “not assessed” due to a lack of recent fish contaminant monitoring at this lake.    The most recent fish tissue monitoring was conducted in 2000.    While these results suggest that levels of contaminants were low at Lower Gar Lake, they are now too old (greater than 10 years) to be used for an assessment.