Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 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 “partially supported” due to algae blooms and high levels of turbidity that violate Iowa’s narrative criteria protecting against aesthetically objectionable conditions.   Violations of the Class A1 criterion for pH also suggest “partial support” of the primary contact recreation uses.   The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH.   Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring at this lake.   Sources of data for this assessment include: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.  

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 2004 through 2008 (approximately 19 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 69, 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 causes an additional impairment at this lake.   The median inorganic suspended solids concentration at Volga Lake was 7.0 mg/L, which was the 31st highest of the 132 monitored lakes.

Data from the 2004-2008 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 73% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (16.3 mg/L) was the 56th highest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH.   Data from the ISU and UHL lake surveys show that during 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 19 samples or dissolved oxygen in 19 samples.   There were, however, 4 violations of the Class A1,B(LW) criterion for pH in 19 samples (21%).  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.   However, Volga Lake was assessed as “partially supporting” in the 2008 assessment/listing cycle due to significant violations of the pH criteria and therefore remains “partially supported” due to the continued violations.    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.   The 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 remain "not assessed" due to the lack of fish contaminant monitoring in this lake.