Iowa DNR
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Water Quality Assessments

Impaired Waters List

Hickory Grove Lake IA 03-SSK-950

Story County S24T83NR22W 2.5 mi SW of Colo.

Assessment Cycle
2008
Release Status
Final
Result Period
2004 - 2006
Designations
Class B(LW) Class A1 Class HH
Assessment Methodology
Assessment Type
Monitored
Integrated Report
Category 5a
Trophic
Eutrophic
Trend
Stable
Legacy ADBCode
IA 03-SSK-00530-L_0
Overall Use Support
Not supporting
Aquatic Life Use Support
Fully
Fish Consumption
Not assessed
Primary Contact Recreation
Not supporting
Documentation
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), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program from 2004 through 2006.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standard.   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 at this lake.   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), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results from the IDNR-county voluntary beach monitoring program from 2004 through 2006.

EXPLANATION: Results of IDNR county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (monitored) as "not supported."  Levels of indicator bacteria at Hickory Grove Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (12 samples), 2005 (14 samples), and 2006 (14 samples) as part of the IDNR county beach monitoring program.   According to IDNR’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) all thirty-day geometric means for 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 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.”  Also, 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 Hickory Grove Lake beach, the geometric means of 3 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 exceeded the Iowa water quality standard of 126 E.  coli orgs/100 ml.   All of the geometric mean violations occurred in 2005.   The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E.  coli orgs/100 ml) was not significantly greater than 10% in any of the following recreation seasons: 2004 (8%), 2005 (14%), or 2006 (21%).   According to IDNR’s assessment methodology and U.S.  EPA guidelines, these results suggest nonsupport of the Class A1 (primary contact recreation) uses at Hickory Grove Lake.

Results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program, however, show good water quality at Hickory Grove Lake.   Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 51, 54, and 55 respectively for Hickory Grove Lake.   According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Hickory Grove Lake in the lower end of the of the eutrophic category.   These values suggest low levels of chlorophyll a and suspended algae in the water, very good water transparency, and low levels of phosphorus in the water column.  

The levels of inorganic suspended solids at this lake were moderately high and do not suggest an impairment due to non-algal turbidity.   The median level of inorganic suspended solids in Hickory Grove Lake (3.2 mg/L) was the 54th lowest median of the 132 lakes sampled by the ISU and UHL programs.

Data from the 2002-2006 ISU and UHL surveys suggest a small population of cyanobacteria exists at Hickory Grove Lake, which does not contribute to impairment at this lake.   These data show that cyanobacteria comprised 70% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (7.3 mg/L) was the 25th lowest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on results from the ISU and UHL lake surveys.  The data from these surveys from 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 17 samples, one violation of the Class B(LW) criterion for dissolved oxygen in 23 samples (4%), and one violation of the Class B(LW) criterion for pH in 23 samples (4%).   Based on IDNR’s assessment methodology these results do not suggest impairment of the Class B(LW) uses at Hickory Grove Lake.

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

Monitoring and Methods
Assessment Key Dates
9/21/2006 Fixed Monitoring End Date
6/3/2002 Fixed Monitoring Start 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)
420 Water column surveys (e.g. fecal coliform)
Monitoring Levels
Biological 3
Habitat 0
Physical Chemistry 3
Toxic 0
Pathogen Indicators 3
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 0
BioIntegrity N/A
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Pathogens Primary Contact Recreation High
  • Source Unknown
  • High
Siltation Aquatic Life Support Not Impairing
  • Agriculture
  • Natural Sources
  • Not Impairing
  • Not Impairing