Arrowhead Lake IA 04-RAC-1136

Assessment Comments

Assessment is based on (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), and (2) results of the statewide ambient lake monitoring program conducted from 2006 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 2006 through 2010 by Iowa State University (ISU), and (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

EXPLANATION:  For the 2012 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 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 48, 48, and 51 respectively for Arrowhead Lake.   According to Carlson (1977) the Secchi depth and chlorophyll a values place Arrowhead Lake in the mesotrophic category while the total phosphorus value places Arrowhead Lake on the lower end of the eutrophic category.   These values suggest extremely 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 4th lowest of the 134 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 (13.5 mg/L) was the 43rd highest of all 134 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 2006-2010 there were no violations of the Class B(LW) criterion for ammonia (21 samples), dissolved oxygen (22 samples), or pH (22 samples).  

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