Assessment Comments
Assessment remains based on results of a diagnostic/feasibility study at Clear Lake conducted by Iowa State University from July 1998 to September 2000.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" based on information from studies conducted by Iowa State University in 1999 and 2000. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this wetland. Because the data from Iowa State University Studies in 1999 and 2000 are now older than five years, the assessment category is changed from a “monitored” (i.e., a higher confidence assessment) to “evaluated” (i.e., lower confidence assessment).
Note: A TMDL for algae and turbidity at Ventura Marsh was prepared and approved by EPA in 2010. Because all of the Section 303(d) impairments identified for the 2010 assessment/listing cycle are addressed by the TMDL, this waterbody is moved to IR Category 4a (impaired; TMDL approved) for the 2010 assessment/listing cycles.
EXPLANATION: The aquatic life uses are assessed as "partially supported" based primarily on information from a study conducted by Iowa State University in 1999 and 2000 as part of the "Clear Lake Diagnostic and Feasibility Study" (Downing et al. 2001). Results of the ISU study suggest that excessive turbidity related to algal biomass and to resuspension of bottom sediments primarily by common carp (but also by black bullheads and possibly wind/wave action) impacts the water clarity, zooplankton composition, and macrophyte distribution of this wetland. Experimental removal of fish populations in this wetland with rotentone resulted in much improved water clarity and increases in the diversity are areal coverage of wetland macrophytes. These positive changes, however, were largely temporary due to recovery of the pre-rotentone fish populations, although some long-term improvement in water quality may have resulted from the expansion of macrophyte beds during the study. The assessment category for this wetland of "monitored" indicates that the assessment is based primarily on recent, site-specific ambient monitoring data and thus have relatively high confidence. IDNR considers waterbodies identified as "impaired" based on "monitored assessments" as candidates for the state's Section 303(d) list.
Fish consumption uses remain "not assessed" due to the lack of data for levels of fish contaminants 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.
