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 in 2006 and 2007 and information from the IDNR Wildlife Bureau.
Basis for Assessment
[NOTES: Prior to the 2002 cycle, the Waterbody ID number for this wetland was IA-WETLAND-17. This wetland is not in the March 2006 version of the Iowa Water Quality Standards but has been proposed for inclusion to the standards as a Class B(LW) waterbody.]
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 Fourmile 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 and 2007 (approximately 13 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 80, and 86 respectively for Fourmile Lake. According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus all place Fourmile Lake in the hypereutrophic category. These values suggest extremely 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.
Additional monitoring of fish and aquatic vegetation populations at Fourmile 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 causing the aquatic life uses to be assessed as "not supported."
NOTE: The water level at Fourmile Lake was lowered in 2007 to begin a restoration project that will renovate fish populations and increase rooted aquatic vegetation at this lake. The goals of this project are to improve wildlife habitat and water quality at this shallow lake.
