Spring Lake IA 04-RAC-1152

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Spring Lake are assessed (monitored) as "not supported" due to poor water transparency 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 70, 64, and 62 respectively for Spring Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Spring Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and moderately high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 15 samples (7%).

Note:A TMDL for turbidity at Spring Lake was prepared by DNR and approved by EPA in 2006.Because the primary Section 303(d) impairment identified for the 2016 assessment/listing cycle (turbidity) is addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) for the 2016 cycle.

The level of inorganic suspended solids was relitivley low at Spring Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Spring Lake (8.2 mg/L) was ranked 112th 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 Spring Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 72% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (59.2 mg/L) was ranked 119th 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 a large population of cyanobacteria. Information from the DNR Fisheries Bureau suggests that nuisance aquatic macrophytes and rough fish remain a concern at this lake.Results of 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 one violation of the criterion for pH in 15 samples(7%). 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 Spring Lake.

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