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 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of IDNR/U.S. EPA fish contaminant monitoring in 2010.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to algae blooms and high levels of turbidity that violate Iowa’s narrative criteria protecting against aesthetically objectionable conditions.   The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish tissue monitoring in 2010.   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 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of IDNR/U.S.  EPA fish contaminant monitoring in 2010.  

EXPLANATION: Results from the ISU and UHL lake surveys suggest that the Class A1 (primary contact recreation) uses at Volga Lake are “partially supported” due to elevated chlorophyll a (algae) levels and high levels of turbidity.   Using the median values from these surveys from 2006 through 2010 (approximately 16 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 64, 66, and 65 respectively for Volga Lake.   According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Volga Lake in between the eutrophic and hypereutrophic categories.   These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and high levels of phosphorus in the water column.  

The level of inorganic suspended solids is high at Volga Lake and suggests that non-algal turbidity contributes to a turbidity impairment at this lake.   The median inorganic suspended solids concentration at Volga Lake was 6.5 mg/L, which was the 36th highest of the 134 monitored lakes.

Data from the 2006-2010 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Volga Lake which contributes algae blooms and aesthetically objectionable conditions at this lake.   These data show that cyanobacteria comprised 63% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (19.1 mg/L) was the 62nd lowest of the 134 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  Data from the ISU and UHL lake surveys show that during 2006-2010 there were no violations of the Class B(LW) criterion for ammonia in 16 samples.   There was one violation of the Class B(LW) criterion for dissolved oxygen in 16 samples (6%).   Based on IDNR's assessment methodology, this violation was not significantly greater than 10% of the samples and therefore does not suggest impairment of the Class B(LW) uses.   There was one violation of the pH criteria in 16 samples (6%).   Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class A1 and Class B(LW) uses at Volga Lake.   Volga Lake was assessed as “partially supporting” in the 2008 assessment/listing cycle due to significant violations of the pH criteria.   Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations.   Because violations of the pH criteria were not significantly greater than 10% for the 2010 assessment/listing cycle or the current (2012) assessment/listing cycle, the pH impairment for Volga Lake is suggested for delisting.   The past pH violations at Volga Lake likely reflect the excessive primary productivity at the lake and do not reflect the input of pollutants into this lake.  

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.   EPA/IDNR fish contaminant (RAFT) monitoring at Volga Lake in 2010.    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: 0.119 ppm.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0948 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 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 2010 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.