Ventura Marsh IA 02-WIN-844

Assessment Comments

Assessment based on results of ISU diagnostic/feasibility study at Clear Lake from July 1998 to September 2000.

Basis for Assessment

SUMMARY:  The Class B(LW) aquatic life uses are assessed (monitored) as "partially supported."  Fish consumption uses remain "not assessed."  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.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.