West Lake (Osceola) IA 04-LDM-1082

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 63, 64, and 72 respectively for West Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place West Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and very high levels of phosphorus in the water column.

The level of inorganic suspended solids was moderately high at West Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in West Lake (3.39 mg/L) was ranked 76th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at West Lake. These data show that cyanobacteria comprised 65% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (6.7 mg/L) was ranked 40th 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 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 2 violations of the criterion for pH in 15 samples(13%). 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 West 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 DNR'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 2012-2016 show that nitrate levels are extremely low at this lake (maximum value = 1.6 mg/l; median = 0.1 mg/l).

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR 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 WestLake.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 DNR and approved by EPA in 2002.