Easter Lake IA 04-LDM-1024

Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Easter Lake Park Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (15 samples), 2013 (14 samples) and 2014 (14 samples), as part of the IDNR beach monitoring program.   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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 Easter Lake Park Beach, the geometric means from 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 12 E.  coli orgs/100 ml in 2012, 24 E.  coli orgs/100 ml in 2013 and 31 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 0% in 2012, 14% in 2013 and 7% in 2014.   None of these are 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 "Fully Supported" of the Class A1 uses.

Easter Lake Park Beach was assessed as "Partially supported" for the 2010 assessment/listing cycle.   Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without violations of the geometric mean criterion and without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on bacteria violations.  There were no violations of the geometric mean criterion for the 2014 or current 2016 assessment listing cycle and there were less than 10% of the samples exceeding the single-sample maximum criterion.   Therefore, the impairment for indicator bacteria is suggested for delisting for the 2016 assessment/listing cycle.

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Easter Lake are assessed (monitored) as "partially 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 67, 63, and 62 respectively for Easter Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Easter Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately 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 nutrients and siltation at Easter Lake was prepared by IDNR and approved by EPA in 2005.   Because all Section 303(d) impairments identified for the 2016 assessment/listing cycle (siltation and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

The level of inorganic suspended solids was high at Easter Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Easter Lake (7.3 mg/L) was ranked 105th 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 Easter Lake. These data show that cyanobacteria comprised 89% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (22.4 mg/L) was ranked 70th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due the impacts of siltation at this lake.   Information from the IDNR Fisheries Bureau also suggests that a poor fishery exists at Easter Lake.  Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), 2 violations of the criterion for dissolved oxygen in 15 samples(13%), 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 Easter Lake.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at Easter Lake in 2005 and 2008.   The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants.   Data from the 2005 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0512 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.026 ppm.   Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.172 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm.   Data from the 2008 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: 0.158 ppm, and technical chlordane: 0.065 ppm.   Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.105 ppm.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   The fish contaminant data generated from the 2005 and 2008 RAFT sampling conducted at Easter Lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.