Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 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” (IR 4a) 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 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 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.  

Note: A TMDL for impairments due to algae and non-algal turbidity at this lake was prepared and approved by EPA in July 2014.  The approval of this TMDL moves the impairments due to algae and non-algal turbidity from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).  

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 2008-2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 69, and 69 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, 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 7.2 mg/L, and ranked 96th of the 134 monitored lakes.

Data from the 2008-2012 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 71% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (17.8 mg/L) and ranked 65th 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 2008-2012 there were no violations of the Class B(LW) criterion for ammonia in 14 samples.   There were three violations of the Class B(LW) criterion for dissolved oxygen in 14 samples (21%).   Based on IDNR's assessment methodology, the frequency of violations 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 14 samples (7%).   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.   Note: Volga lake was listed as impaired for violations to the water quality criteria in the 2008 assessment/lising cycle and suggested for de-listing in the 2012 assessment/listing cycle.   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.