West Lake (Osceola) IA 04-LDM-1082

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." 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 70, 65, and 74 respectively for West Lake (Osceola). According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place West Lake (Osceola) in between the Eutrophic and the Hypereutrophic categories. These values suggest 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 level of inorganic suspended solids was relatively low at West Lake (Osceola), and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in West Lake (Osceola) (2.5 mg/L) was ranked 39th 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 West Lake (Osceola). These data show that cyanobacteria comprised 76% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.1 mg/L) was ranked 57th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." 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 3 violations of the criterion for pH in 15 samples(20%). 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 West Lake (Osceola). 

West Lake (Osceola) was assessed as "not supported" for the 2008 assessment/listing cycle. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on dissolved oxygen violations.  There were less than 10% of the samples exceeding the single-sample maximum criterion for both the 2014 and 2016 assessment/listing cycles.   Therefore, the impairment (5a) for dissolved oxygen is suggested for delisting for the 2016 assessment/listing cycle.

Information from the IDNR Fisheries Bureau suggests that West Lake (Osceola) does experience severe algae blooms during the summer.  However, the Municipal Utilities treat the lake with copper sulfate to suppress the algae, which may affect sampling by the ISU survey.  Information from the IDNR Fisheries Bureau also suggests that common carp affect water quality at this lake.  

The Class C (drinking water) uses are assessed (monitored) as "fully supported" based primarily on results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" from 2010 through 2012.  Results of this monitoring showed no violations of Iowa’s Class C water quality criterion for atrazine of 3 ug/l in the 63 samples collected from 2010-12 (maximum value:  2.93 ug/l).   Not surprisingly, none of the 63 moving annual averages for this monitoring period exceeded the Class C criterion (maximum moving annual average = 1.45 ug/l).    Based on IDNR's assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported." In addition results of the ISU surveys from 2010-2014 show that nitrate levels are relatively low at this lake (maximum value = 1.6 mg/l; median = 0.2 mg/l) relative to the MCL (10 mg/L). 

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.   EPA/IDNR fish contaminant (RAFT) monitoring at West Lake (Osceola) in 2013.    The composite samples of fillets from largemouth bass and channel catfish had low levels of contaminants.    Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.253 ppm.    Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.05 ppm; total PCBs: <0.15 ppm; and technical chlordane: <0.2 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 2013 RAFT sampling conducted at this 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. Follow-up sampling was conducted in 2014 and suggests "full support" of fish consumption uses at West Lake.  The composite samples of fillets from largemouth bass fillets were as follows: mercury: 0.139 ppm, which is below the advisory threshold.

Note: A TMDL for atrazine at West Lake (Osceola) Osceola was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 through the 2010 Integrated Reporting cycles.  Because atrazine levels had been low over the 2004-2012 monitoring period and had shown "full support" of the Class C uses for the 2008, 2010, 2012, and 2014 Integrated Reporting cycles, this impairment was removed, and the Class C uses were moved from Category 4a (impaired; TMDL not required) to Category 2a (fully supported) of Iowa's Integrated Report.