Dale Maffitt Reservoir IA 04-RAC-1119

Polk County S31T78NR25W at SW edge of Des Moines.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

Open Segment Map
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Cycle: 2018
Release Status: Final
Overall IR: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trophic: Mesotrophic
Trend: Stable
Created: 3/14/2019 12:58:02 PM
Updated: 3/14/2019 12:59:23 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class C

Drinking Water -

Not Assessed

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

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.

Assessment Explanation

For the 2018 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. This is the same assessment as used for 2012, 2014, and 2016 assessment/listing cycles.

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.

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

Monitoring and Methods

Assessment Key Dates

5/30/2006

Fixed Monitoring Start Date

8/1/2007

Fixed Monitoring End Date

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)