Dale Maffitt Reservoir IA 04-RAC-1119

Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2007 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as “fully supported.”  The Class B(LW) (aquatic life) uses are assessed (evaluated) as “fully supported.” In terms of nutrient condition and water transparency, this lake continues to demonstrate exceptional water quality.   Fish consumption uses remain “not assessed.”  Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2007 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.

NOTE: Monitoring at this lake was discontinued in 2008 due to access issues.   Dale Maffit is a public drinking water supply without boating access.

EXPLANATION: For the 2012 reporting cycle, the Class A1 (primary contact recreation) uses for Dale Maffit Lake are assessed as “fully supported” based on results from the ISU statewide survey of lakes.   Using the median values from this survey from 2006 through 2007 (approximately 6 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 48, 47, and 41 respectively for Dale Maffit Lake.   According to Carlson (1977) the index values for Secchi depth, chlorophyll a, and total phosphorus all place Dale Maffit Lake in the mesotrophic category.   These values suggest extremely low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and extremely low levels of phosphorus in the water column.  

The levels of inorganic suspended solids at this lake were very low and do not suggest that non-algal turbidity causes water quality problems at this lake.   The median level of inorganic suspended solids in Dale Maffit Lake (2.0 mg/L) was the 11th lowest median of the 134 lakes sampled by the ISU and UHL surveys.

Data from the 2006-2007 ISU survey suggests that cyanobacteria were relatively low at Dale Maffit Lake and do not suggest an impairment at this lake.   These data show that cyanobacteria comprised 98% of the phytoplankton wet mass at this lake.   However, the median cyanobacteria wet mass (10.8 mg/L) was the 28th lowest of the 134 lakes sampled.  

The Class B(LW) (aquatic life) uses for Dale Maffit Lake are assessed (evaluated) as “fully supported.”  The ISU lake survey data from 2006-2007 show no violations of the Class B(LW) criterion for ammonia in 6 samples, dissolved oxygen in 6 samples, or pH in 6 samples.  These results suggest "full support" of the Class B(LW) uses at Dale Maffit Lake.

The Class C (drinking water) uses remain "not assessed" due to lack of information upon which to base an assessment.   The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate.   While the results of the ISU survey from 2006-07 show that nitrate levels are extremely low at this lake (maximum value = 0.6 mg/l; median = 0.3 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.    

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