Arrowhead Lake IA 04-RAC-1136

Sac County S4T86NR36W S edge of Lake View.

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: 1/29/2019 9:12:48 AM
Updated: 1/29/2019 9:18:22 AM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

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 of Arrowhead Lake 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 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.

Assessment Explanation

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Arrowhead Lake (Sac) are assessed (monitored) as "fully supported" based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 50, 51, and 49 respectively for Arrowhead Lake (Sac). According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Arrowhead Lake (Sac) in between the Mesotrophic and the Eutrophic categories. These values suggest low levels of chlorophyll a and suspended algae in the water, very good water transparency, and extremely low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was extremely low at Arrowhead Lake (Sac), and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Arrowhead Lake (Sac) (1.05 mg/L) was ranked 2nd among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at Arrowhead Lake (Sac). These data show that cyanobacteria comprised 84% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (10 mg/L) was ranked 47th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Arrowhead Lake (Sac).

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

Monitoring and Methods

Assessment Key Dates

5/17/2012

Fixed Monitoring Start Date

8/16/2016

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)