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 information from the IDNR Wildlife Bureau.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses are assessed (evaluated) as "not supported" based on water quality data collected as part of the DNR's shallow lakes and wetlands monitoring program and information from the IDNR Wildlife Bureau. 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.
EXPLANATION: Results of water quality monitoring conducted at Diamond Lake indicate that the aquatic life uses should be assessed (evaluated) as "not supported" due to high levels of algae and turbidity at this lake. Using the median values from this survey from 2006 (approximately 6 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 71, 81, and 85 respectively for Diamond Lake. According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus all place Diamond 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 Diamond 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 and therefore cause the aquatic life uses to be assessed as "not supported." Because only one year of water quality data was collected this assessment is considered "evaluated" indicating relatively low confidence rather than "monitored." Therefore this lake will be added to Iowa's list of waters in need of further investigation.
NOTE: The water level at Diamond 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.
