Dale Maffitt Reservoir IA 04-RAC-1119

Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 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 (monitored) as “fully supported.”  The Class B(LW) (aquatic life) uses are assessed (monitored) 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 2002 through 2006 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.

EXPLANATION: For the 2008 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 2002 through 2006 (approximately 15 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 43, 41, and 43 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 moderately high but 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 (3.6 mg/L) was the 75th highest median of the 132 lakes sampled by the ISU and UHL surveys.

Data from the 2002-2006 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 99% of the phytoplankton wet mass at this lake.   However, the median cyanobacteria wet mass (11.5 mg/L) was the 41st lowest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses for Dale Maffit Lake are assessed (monitored) as “fully supported.”  The ISU lake survey data from 2002-2006 show no violations of the Class B(LW) criterion for ammonia in 8 samples, or dissolved oxygen in 14 samples.   The ISU survey does show one violation of the Class B(LW) criterion for pH in 15 samples (7%).   According to IDNR’s assessment methodology this one violation is not significantly greater than 10% of the samples and therefore does not constitute an impairment to the Class B(LW) uses of 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 2002-06 show that nitrate levels are extremely low at this lake (maximum value = 0.6 mg/l; median = 0.1 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.