Assessment Comments
Assessment remains based on: (1) results of a fish kill investigation in August 2006, and (2) results of DNR/EPA RAFT fish tissue monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain not assessed due to a lack of information upon which to base an assessment. The Class B(LW) (aquatic life) uses remain assessed (evaluated) as "partially supported" due to a fish kill in August 2006. The fish consumption uses remain assessed (evaluated) as "fully supported" based on results of EPA/IDNR fish contaminant monitoring in 2001.
EXPLANATION: The Class A1 (primary contact recreation) uses remain not assessed due to a lack of information upon which to base an assessment. The Class B(LW) (aquatic life) uses remain assessed (evaluated) as "partially supported" due to a fish kill. The fish kill occurred on or before August 2, 2006. No detailed counts were made, but approximately 2,000 fish were estimated to have been killed. Large numbers common carp, crappie (black and white), largemouth bass, channel catfish, and green sunfish were observed.
The cause of the kill was attributed to a natural summer kill. Water quality parameters indicated low oxygen conditions were present. At approximately 9:00 AM August 3 city officials recorded surface oxygen concentrations of 1.7 mg/l. An oxygen profile taken at approximately 12:00 PM indicated a surface oxygen concentration of 3.0 mg/l, 2.7 mg/l at 2 feet, 1.2 mg/l at 4 feet and 0.16 mg/l at 6 feet. Temperatures ranged from 83.7 degrees on the surface to 73.4 degrees below the thermocline at 6 feet. Observations suggest that a recent algae bloom was actively decomposing, and likely resulted in these low oxygen conditions.
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 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. Thus, the 2006 fish summer kill at the Ottumwa Park Ponds is appropriate for IR category 2b.
Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Ottumwa Park Ponds in 2001. 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 composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. 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 2001 RAFT sampling conducted at Ottumwa Park Ponds showed that the levels of contaminants do not exceed any of the IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
