Assessment Comments
Assessment is based on results of water quality, aquatic vegetation, and fish monitoring conducted by the IDNR shallow lakes and wetlands monitoring program from 2006 through 2008 and information from the IDNR Wildlife Bureau.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses are assessed (monitored) as "not supported" due to poor water clarity caused by high levels of turbidity and algae in the water column. The fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.
EXPLANATION: Results of water quality monitoring conducted at Virgin Lake indicate that the aquatic life uses should be assessed (monitored) as "not supported" due to high levels of algae and turbidity at this lake. Using the median values from this survey from 2006 through 2008 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 80, 83, and 85 respectively for Virgin Lake. According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus all place Virgin Lake in the hypereutrophic category. These values suggest extremely high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column.
Additional monitoring of fish and aquatic vegetation populations at Virgin Lake suggest that the high levels of algae and turbidity have adverse effects on fish populations and limit the production of rooted aquatic vegetation in this wetland and therefore cause the aquatic life uses to be assessed as "not supported."
