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: This lake is not designated for Class A1 primary contact recreation uses. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to high levels of pH that exceed state criteria. Poor water transparency due to algae and inorganic turbidity (suspended solids) have led to a poor fishery that also causes an impairment of the aquatic life uses. 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: For the 2010 reporting cycle, the Class B(LW) uses for Avenue of the Saints Lake are assessed (monitored) as “partially supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. The water chemistry data from the ISU and UHL lake surveys show no violations of the Class B(LW) criteria for ammonia in 22 samples, or dissolved oxygen in 22 samples. The pH data, however, show 6 violations of the Class B(LW) criterion in 22 samples. Based on IDNR’s assessment methodology these results are significantly greater than 10% of the samples and therefore suggest an impairment (partial support/monitored) of the Class B(LW) uses of Avenue of the Saints Lake. These violations, however, likely reflect the excessive primary productivity at Avenue of the Saints and do not reflect the input of pollutants into this lake.
Information from the DNR Fisheries Bureau also suggests that the Class B(LW) uses be assessed as “partially supported.” Poor water clarity due to algal and non-algal turbidity, water level fluctuations, an no aquatic vegetation have led to a poor fishery at Avenue of the Saints Lake.
Using the median values from these surveys from 2004 through 2008 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 68, and 77 respectively for Avenue of the Saints Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Avenue of the Saints Lake in the hypereutrophic category while the chlorophyll a value places Avenue of the Saints Lake between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were high and suggest water quality problems exist related to non-algal turbidity. The median level of inorganic suspended solids in Avenue of the Saints Lake (6.4 mg/L) was the 39th highest level of the 132 lakes monitored by the ISU and UHL programs.
Data from the 2004-2008 ISU and UHL surveys suggest a large population of cyanobacteria exists at Avenue of the Saints Lake, which contributes to water quality problems at this lake. These data show that cyanobacteria comprised 85% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (44.6 mg/L) was also the 22nd highest of the 132 lakes sampled. This median is in the worst 25% of the 132 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2004-2008 period. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
