Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2007 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water transparency due to both non-algal turbidity and algae. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are "not assessed" based on a lack of recent information upon which to base an assessment. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2007 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
Note: A TMDL for algae and turbidity at Five Island Lake was prepared by IDNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2008, 2010, and current (2012) assessment/listing cycle (algal growth and turbidity) are addressed by the TMDL, this waterbody remains in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2012 reporting cycle, the Class A1 (primary contact recreation) uses for Five Island Lake are assessed (monitored) as “not supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 65, and 68 respectively for Five Island Lake. According to Carlson (1977) the Secchi depth value places Five Island Lake in the hypereutrophic category, while the chlorophyll a and total phosphorus values place Five Island Lake 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 high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were very high and suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Five Island Lake (12.0 mg/L) was the 12th highest median of the 134 lakes sampled by the ISU and UHL programs.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Five Island Lake, which contributes to the aesthetically objectionable conditions at this lake. These data show that cyanobacteria comprised 55% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (30.3 mg/L) was the 50th highest of the 134 lakes sampled. This potential impairment is appropriate for Category 3b of Iowa's 2012 Integrated Report and will be placed on Iowa's list of waters in need of further investigation.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau, and results of the ISU and UHL lake surveys. The ISU and UHL lake surveys data from 2006-2010 show no violations of the Class B(LW) criteria for ammonia in 21 samples, no violations of the Class B(LW) criterion for dissolved oxygen in 22 samples, and no violations of the Class A1,B(LW) criterion for pH in 22 samples. Based on IDNR’s assessment methodology these results suggest full support of the Class B(LW) uses at Five Island Lake. According to the IDNR Fisheries Bureau water quality has improved at Five Island Lake due to a lake dredging project.
Fish consumption uses were “not assessed” due to a lack of recent fish contaminant monitoring at this lake. The most recent fish tissue monitoring was conducted in 2001. While these results suggest that levels of contaminants were low at Five Island Lake, they are now too old (greater than 10 years) to be used for an assessment.
