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 and 2006 by University Hygienic Laboratory (UHL), (3) results from the IDNR-county voluntary beach monitoring program from 2004, and (4) 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.” The Class C (drinking water) uses remain “not assessed” due to a lack of monitoring data. Fish consumption uses remain “not assessed” due to lack of recent information on which to base an assessment. 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 and 2006 by University Hygienic Laboratory (UHL), (3) results from the IDNR-county voluntary beach monitoring program from 2004, and (4) information from the IDNR Fisheries Bureau.
Note: A TMDL for siltation at Lake Icaria was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 and 2006 assessment/listing cycles. Data for the 2008 assessment show that water quality has improved; therefore Lake Icaria is placed into IR Category 2a (some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met) for the 2008 assessment/listing cycle.
EXPLANATION: Results of IDNR county beach monitoring from 2004 suggest that the Class A1 uses are assessed (evaluated) as "fully supported." Levels of indicator bacteria at Lake Icaria beach were monitored approximately once per week during the primary contact recreation season (May through August) of 2004 (13 samples) as part of the IDNR county beach monitoring program. Because there was only one year of data collected at Lake Icaria beach, this assessment is considered “evaluated”, which is of lower confidence than a monitored assessment. 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 Lake Icaria beach, the geometric means of all 9 thirty-day periods during the summer recreation season of 2004 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was also less than 10% in 2004 (8%). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support (evaluated) of the Class A1 (primary contact recreation) uses.
Results from the ISU lake survey and the UHL ambient lake monitoring program also suggest that the Class A1 (primary contact recreation) uses for Lake Icaria be assessed (monitored) as “fully supported” for the 2008 reporting cycle. Using the median values from these surveys from 2002 through 2006 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 56, 49, and 61 respectively for Lake Icaria. These results show a significant improvement over the 2006 assessment where the trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 57, and 63 respectively. These improvements are likely due to a fisheries renovation completed in fall 2004 that eliminated yellow bass from the lake and reduced the common carp population. Extensive soil conservation practices in the watershed along with shoreline stabilization efforts have also likely led to improved water quality. The trophic state index differences from the 2006 assessment to the 2008 assessment show a decrease in chlorophyll a and suspended algae in the water, and an increase in water transparency that suggest that the Class A1 uses are fully supported.
According to Carlson (1977) the 2008 assessment Secchi depth value places Lake Icaria in the eutrophic category, while the chlorophyll a value places Lake Icaria in the mesotrophic category. The total phosphorus value places Lake Icaria in between the eutrophic and hypereutrophic categories. These values suggest low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and moderately high levels of phosphorus in the water column.
Inorganic suspended solids are high at Lake Icaria and indicate that non-algal turbidity remains a water quality concern. Based on data from the ISU and UHL surveys from 2002 through 2006, the median concentration of inorganic suspended solids at Lake Icaria was 6.6 mg/L, which was the 41st highest concentration of the 132 lakes monitored by these programs.
Data from the 2002-2006 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Lake Icaria, which does not contribute to impairment at this lake. These data show that cyanobacteria comprised a significant portion (84%) of the phytoplankton wet mass at this lake. However, the median cyanobacteria wet mass (9.5 mg/L) was the 30th lowest of the 132 lakes sampled.
An additional factor that could account for the low chlorophyll a TSI score and low median cyanobacteria wet mass is the application of copper sulfate to Lake Icaria. The City of Corning applies copper sulfate (an algaecide) to Lake Icaria in the event of an algae bloom (Iowa Water Web).
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “fully supported” based on information from IDNR’s Fisheries Bureau and results of the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau indicates that extensive soil conservation practices have been implemented in the watershed that likely will reduce nutrient loading and siltation impacts in Lake Icaria. A fish renovation in fall 2004 also contributes to improved water quality at this lake.
Results of the ISU and UHL lake surveys also suggest generally good chemical water quality and “full support” of the Class B(LW) uses at Lake Icaria. The ISU and UHL lake survey data from 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 13 samples and no violations of the Class A1,B(LW) criterion for pH in 19 samples. The data show 3 violations of the Class B(LW) criterion for dissolved oxygen in 20 samples (15%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment (full support/monitored) of the aquatic life uses at this lake.
Drinking water (Class C) uses were not assessed due to the lack of water quality information upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2002-06 show that nitrate levels at this lake (maximum value = 3.6 mg/l; median = 0.8 mg/l in 19 samples) are low relative to the drinking water MCL (10 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are “not assessed” due to the lack of recent information upon which to base an assessment. The most recent fish contaminant monitoring at this lake was conducted in 1993 as part of the U.S. EPA/IDNR fish tissue (RAFT) monitoring program. Although results of the 1993 RAFT monitoring indicated very low levels of contaminants and “full support” of the fish consumption uses, these data are now considered too old (greater than 10 years) to characterize current water quality conditions.
