Big Wall Lake IA 02-IOW-656

Assessment Comments

Assessment remains based on information from the IDNR Wildlife Bureau.

Basis for Assessment

SUMMARY:  The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to water level stabilization.   Fish consumption uses remain "not assessed."  This is the same assessment as that developed for the 2004 and 2006 assessment/listing cycles.   Information from IDNR staff indicate that a control structure will be installed in early 2007, thus allowing the ability to manipulate the water level and thus improve water quality conditions at this wetland.

EXPLANATION:  The aquatic life uses remain assessed as "partially supported" based on information from the Iowa DNR Wildlife Bureau (see assessment for the 1998 and 2000 reports).   A site visit in October 2000 by IDNR staff and EPA Region VII staff indicates that this wetland does not have a siltation impairment but suffers from (1) an inability to manipulate the water level and (2) a large population of common carp that moved in to the wetland during the high waters of 1993.   Common carp are believed to have caused reduction in growth and areal coverage of wetland macrophytes either through grazing on young plants or through increased turbidity that results in light limitation and shading-out of some macrophytes.   Well-timed manipulation of the water level would allow drawdown of the wetland during winter to allow a winterkill of the nuisance population of common carp, thus allowing re-establishment of the desired wetland macrophytes.  

The assessment category for this wetland of "evaluated" indicates that the assessment is based entirely on "best professional judgement."  In terms of Section 305(b) reporting, "monitored assessments" are 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.   "Evaluated assessments" are those based on data older than five years or other than site-specific ambient monitoring data (e.g., questionnaire surveys of fish and game biologists [=best professional judgement]).   IDNR does not consider waterbodies identified as "impaired" based on "evaluated assessments" as candidates for the state's Section 303(d) list.  

A watershed project now exists for Big Wall Lake (see the project web site at http://www.iowadnr.gov/water/watershed/bigwalllake/about.html).   This is a cooperative project between Iowa DNR, the Iowa Department of Agriculture & Land Stewardship/Division of Soil Conservation, and the federal Natural Resources Conservation Service.   The following information is from the project web site:

"In 2006, the Wright County Soil and Water Conservation District completed an inventory of the potential causes of watershed degradation of Big Wall Lake, and presented possible solutions to landowners, cabin owners and recreational users of the lake.  A partial drawdown of the lake in the winter of 2005-2006 was the jump-start of the project, and was followed by a series of chemical treatments in June 2007 to remove the carp.  The design of the project included the installation of a water control structure with stop logs to control the water levels in the lake.  Rodent guards were placed on both ends of the structure and a second channel was constructed to extend the lake."

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this wetland.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.