Assessment Comments
Assessment remains based on information from the IDNR Wildlife Bureau and results of water quality monitoring water quality, aquatic vegetation, and fish monitoring conducted by the IDNR shallow lakes and wetlands monitoring program from 2006 through 2008.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses are assessed (evaluated) as "not supported" due to high levels of algae in the water column. Fish consumption uses remain "not assessed." NOTE: Information from IDNR staff indicate that a control structure was installed in early 2007, thus allowing the ability to manipulate the water level and thus improve water quality conditions at this wetland. Therefore the impairment for flow alteration has been removed at this lake.
EXPLANATION: The aquatic life uses are assessed (evaluated) as "not supported" based on results of water quality monitoring conducted by the IDNR shallow lakes and wetland monitoring program. Results of water quality monitoring conducted at Big Wall Lake in 2008 and 2009 indicate that the aquatic life uses should be assessed (monitored) as "not supported" due to high levels of algae at this lake. Using the median values from this survey from 2008 and 2009 (approximately 7 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 70, and 104 respectively for Big Wall Lake. According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus all place Big Wall Lake in the hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column.
Because only 2 chlorophyll samples were collected during 2008 due to water level drawdowns, the 2009 data was included in this assessment. However, the 2008 and 2009 data is still insufficient to characterize water quality at Big Wall Lake. Therefore, this assessment is considered "evaluated" or of lower confidence and is therefore not a candidate for section 303d listing.
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.
