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, (4) results of U.S. EPA/IDNR fish tissue monitoring in 1999, and (5) results of a fish kill investigation in May 2007.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water transparency and algal blooms that violate the state’s narrative criteria protecting against aesthetically objectionable conditions. High levels of pH that exceed state criteria also contribute to the impairment as well as the presence of nuisance aquatic life (cyanobacteria). The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” primarily due to high levels of pH that exceed state criteria and results of a fish kill investigation in May 2007. Fish consumption uses remain assessed (evaluated) “fully supported.” 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, (4) results of U.S. EPA/IDNR fish tissue monitoring in 1999, and (5) results of a fish kill investigation in May 2007.
Note: A TMDL for siltation and nutrients at Badger Creek Lake was prepared by IDNR and approved by EPA in 2003. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (algal growth [inlcuding nuisance growth of cyanobacteria] and pH) are addressed by the TMDL, this waterbody remains in IR Category 4a (TMDL approved).
EXPLANATION: For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Badger Creek Lake are assessed as “not supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. 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 75, 70, and 81 respectively for Badger Creek Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Badger Creek Lake in the hypereutrophic category. These values suggest very 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 very high and suggest that high levels of non-algal turbidity contribute to the impairment at this lake. The median level of inorganic suspended solids in Badger Creek Lake (7.8 mg/L) was the 33rd highest median for all the 132 lakes sampled by ISU and UHL.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Badger Creek Lake, which contributes to the impairment at this lake. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (63.0 mg/L) was also the 18th 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 2002-2006 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.
The Class B(LW) (aquatic life) uses for Badger Creek Lake are assessed (monitored) as “partially supported” based on information from the IDNR Fisheries Bureau, results of a fish kill investigation, and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that algal blooms and water clarity remain problems at this lake. The ISU and UHL lake surveys data from 2002-2006 show no violations of the Class B(LW) criterion for ammonia in 14 samples. The data show 3 violations of the Class B(LW) criterion for dissolved oxygen in 20 samples. Based on IDNR’s methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses of Badger Creek Lake. The data also show 6 of 20 samples violated the Class B(LW) criterion for pH (30%). Based on IDNR’s methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (partial supported/monitored) of the Class A1 and Class B(LW) uses of Badger Creek Lake. These water quality violations, however, likely reflect the excessive primary productivity at Badger Creek Lake and do not reflect the input of pollutants to this lake.
A fish kill that occurred in this lake on or before May 17, 2007 also suggests "impairment" of the Class B(LW) uses. The kill was identified as a natural kill related to spawning stress. Monitoring of the lake showed that the pH was high (9.2) and there was a large amount of brown algae in the lake. The total number of fish killed was estimated to be 1000. According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Fish consumption uses are assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Badger Creek Lake in 1999. The composite samples of fillets from channel catfish and black crappie had low levels of contaminants. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 1999 RAFT sampling conducted in this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
