Spring Lake IA 04-RAC-1152

Results of IDNR county beach monitoring from 2008 suggest that the Class A1 uses are assessed (evaluated) as "fully supported."  Levels of indicator bacteria at Spring Lake beach were monitored approximately once per week during the primary contact recreation season (May through August) of 2008 (5 samples) as part of the IDNR county beach monitoring program.   Because a limited number of samples were collected in 2008 these data are considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E.  coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E.  coli orgs/100 ml.   If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.”  Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E.  coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.”  This assessment approach is based on U.S.   EPA guidelines (see pgs 3-33 to 3-35 of U.S.   EPA 1997b).    

At Spring Lake beach, the geometric mean from 2008 was below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 16 E.  coli orgs/100 ml in 2008.   The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E.  coli orgs/100 ml) was 0% in 2008.   These results are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses.    According to IDNR’s assessment methodology and U.S.  EPA guidelines, these results suggest “full support” of the Class A1 uses.

However, for the 2016 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 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 71, 62, 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. IDNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment.   The chlorophyll a TSI value for the 2008 assessment listing cycle was 69, which based on IDNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions.   Because the TSI value for the 2014 assessment/listing cycle was less than the trigger of 65 (2014 listing for chlorophyll a was 61), and because the TSI value for the current listing cycle is also 62, based on IDNR's methodology, the impairment for chlorophyll a is suggested for delisting from catagory 4a for the 2016 assessment/listing cycle.

Note:  A TMDL for turbidity at Spring Lake was prepared by IDNR 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 high at Spring Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Spring Lake (7 mg/L) was ranked 103rd among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 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 84% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (61.6 mg/L) was ranked 121st 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 2010-2014. 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 IDNR Fisheries Bureau suggests that nuisance aquatic macrophytes and rough fish remain a concern at this lake. 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 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 Spring Lake.

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