Arrowhead Lake IA 04-RAC-1136

Assessment Comments

Assessment is based on (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), and (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported.”  The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  Fish consumption uses remain “not assessed” due to a lack of fish contaminant monitoring.   Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), and (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

EXPLANATION:  For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Arrowhead Lake are assessed as “fully supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program.   Using the median values from these surveys from 2004 through 2008 (approximately 25 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 49, 51, and 53 respectively for Arrowhead Lake.   According to Carlson (1977) the Secchi depth value places Arrowhead Lake in the mesotrophic category while the chlorophyll a and total phosphorus values place Arrowhead Lake on the lower end of the eutrophic category.   These values suggest low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and low levels of phosphorus in the water column.  

The level of inorganic suspended solids is also low at this lake and does not suggest water quality problems due high non-algal turbidity.   The median inorganic suspended solids concentration at Arrowhead Lake was 2.0 mg/L, which was the 15th lowest of the 132 monitored lakes.

The presence of nuisance algae populations at this lake does not appear to be a problem.   Data from the ISU and UHL lake surveys show that the median cyanobacteria wet mass at Arrowhead Lake (22.1 mg/L) was the 46th highest of all 132 monitored lakes.

The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on results from the ISU and UHL lake surveys.   The ISU and UHL lake survey results show good chemical water quality at Arrowhead Lake.   During 2004-2008 there were no violations of the Class B(LW) criterion for ammonia (24 samples), dissolved oxygen (25 samples), or pH (25 samples).  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.