Rodgers Park Lake IA 02-CED-526

Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

Basis for 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 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

EXPLANATION: Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Rodgers Park Lake are “fully supported.”  Using the median values from these surveys from 2004 through 2008 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 64, and 67 respectively for Rodgers Park Lake.   According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Rodgers Park Lake in between the eutrophic and hypereutrophic categories.   These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and high levels of phosphorus in the water column.  

The level of inorganic suspended solids is moderately high at this lake and does not suggest an impairment due to high non-algal turbidity.   The median inorganic suspended solids concentration at Rodgers Park Lake was 4.0 mg/L, which was the 64th highest of the 132 monitored lakes.

Data from the 2004-2008 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Rodgers Park Lake, which does not contribute to impairment at this lake.   These data show that cyanobacteria comprised only 26% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (3.9 mg/L) was the 21st lowest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau, and results from the ISU and UHL lake surveys.   The ISU and UHL lake surveys suggest relatively good chemical water quality at Rodgers Park Lake.   Data from these surveys show that during 2004-2008 show there were no violations of the Class B(LW) criterion for ammonia in 20 samples or dissolved oxygen in 20 samples.   Data for pH showed 3 violations of the criterion in 20 samples (15%).   Based on IDNR’s assessment methodology the pH violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses at Rodgers Park Lake.

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