Green Castle Lake IA 02-IOW-643

Marshall County S8T82NR17W 1 mi. S of Ferguson.

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: Eutrophic
Trend: Unknown
Created: 3/15/2019 9:21:02 AM
Updated: 3/15/2019 9:23:07 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 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.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2010 through 2014 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 Green Castle Lake 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 9 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 55, 59, and 58 respectively for Green Castle Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Green Castle Lake in the Eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and relatively low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 9 samples.

The level of inorganic suspended solids was low at Green Castle Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Green Castle Lake (1.1 mg/L) was ranked 8th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a small population of cyanobacteria exists at Green Castle Lake. These data show that cyanobacteria comprised 8% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (0.6 mg/L) was ranked 5th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 9 samples(0%), no violations of the criterion for dissolved oxygen in 9 samples(0%), and no violations of the criterion for pH in 9 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/evaluated) of the Class B(LW) uses of Green Castle Lake.

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

Note: Green Castle Lake was drained in 2013. Common carp and silt were removed from the lake and fish habitat improvements were made. Improvements in water clarity were observed in 2015 sampling season after the lake refilled.

Monitoring and Methods

Assessment Key Dates

6/18/2012

Fixed Monitoring Start Date

9/20/2016

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)