Pleasant Creek Lake IA 02-CED-459

Linn County S31T85NR8W 4 mi. NNW of Palo.

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.

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Cycle: 2018
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 10/16/2018 10:52:14 AM
Updated: 4/22/2019 2:19:13 PM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2012

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier II

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Fully Supported

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 “partially supported” due to violations of the criterion for indicator bacteria. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses remained assessed (monitored) as "fully supporting" based on the results of fish contaminant monitoring in 2009. Sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2013 through 2016, (2) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2009.

Assessment Explanation

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Pleasant Creek Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (15 samples), 2015 (19 samples) and 2016 (6 samples), as part of the DNR beach monitoring program. According to DNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state's geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state's single-sample maximum value of 235 E. coli orgs/100 ml. If a sampling season geometric mean exceeds the state criterion of 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa's single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).

At Pleasant Creek Beach, the geometric means from 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 13 E. coli orgs/100 ml in 2014, 66 E. coli orgs/100 ml in 2015 and 13 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2014, 11% in 2015 and 0% in 2016. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses.

While the levels of indicator bacteriaforPleasant Creek Beach are not significantly greater than 10% of the samples and do not exceed the state's single-season geometric mean criterion of 126 E. coli orgs/100 ml for the 2016 and 2018 reporting cycle, Pleasant Creek Beach was listed as "partially supporting" the ClassA1uses for the 2014reporting cycle due to indicator bacteria. According to DNR's methodology, lakes must meet (monitored) water quality standards for two consecutive assessment/listing cycles to suggest de-listing. Therefore, the Class A1 uses will remain listed as "partially supported" for the 2018 cycle.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Pleasant Creek 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 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 52, 61, and 56 respectively for Pleasant Creek Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Pleasant Creek Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very 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 15 samples.

The level of inorganic suspended solids was low at Pleasant Creek Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Pleasant Creek Lake (1.6 mg/L) was ranked 9th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Pleasant Creek Lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (17.4 mg/L) was ranked 63rd 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%), 3 violations of the criterion for dissolved oxygen in 15 samples(20%), 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 Pleasant Creek Lake.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/DNR fish contaminant (RAFT) monitoring at Pleasant Creek Lake in 2009. The composite samples of fillets from largemouth bass and channel catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.042 ppm. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.212 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2009 RAFT sampling conducted at this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.

Monitoring and Methods

Assessment Key Dates

6/19/2012

Fixed Monitoring Start Date

9/21/2016

Fixed Monitoring End Date

7/16/2009

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

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

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)