Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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 algae blooms 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 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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 levels.   Using the median values from these surveys from 2002 through 2006 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 69, and 66 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 only moderately high at Volga Lake and does not suggest an impairment due to non-algal turbidity.   The median inorganic suspended solids concentration at Volga Lake was 5.8 mg/L, which was the 49th highest of the 132 monitored lakes.

Data from the 2002-2006 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Volga Lake which contribute to the impairment at this lake due to algae blooms.   These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (19.0 mg/L) was the 65th 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 2002-2006 there were no violations of the Class B(LW) criterion for ammonia in 14 samples or dissolved oxygen in 19 samples.   There were, however, 7 violations of the Class A1,B(LW) criterion for pH in 20 samples (35%).  Based on IDNR’s assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest an impairment of the Class A1 and Class B(LW) uses at Volga Lake.  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.