Assessment Comments
Assessment remains based on (1) information from the IDNR Wildlife Bureau and (2) results of an IDNR investigation of a fish kill in Little Swan Lake in April 2004.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses of this waterbody remain assessed (evaluated) as “partially supported” due to a fish kill in Little Swan Lake in April 2004. The kill was attributed to natural causes. This impairment is appropriate for Category 3b of Iowa’s Integrated Report. Based on information from the IDNR Wildlife Bureau, however, the aquatic life uses should be assessed (evaluated) as "fully supported". Fish consumption uses remain "not assessed."
EXPLANATION: According to the IDNR Wildlife Bureau, the aquatic life uses of this wetland should be assessed (evaluated) as "fully supported". Despite this information, a fish kill in April 2004 in Little Swan Lakes suggests that the aquatic life uses of this wetland should be assessed (evaluated) as only "partially supported". This kill occurred on April 29, 2004; the cause of the kill was identified as natural/winterkill. An estimated 30 fish were killed including common carp, channel catfish and yellow perch. No estimate of the value of the fish killed was provided. Little Swan Lake is part of the “Swan Lake and Christopherson Slough State Wildlife Management Area in northeastern Dickinson County. According to the IDNR investigation, a fish survey following the kill showed live fish in Little Swan Lake (i.e., bullheads, carp, buffalo, crappie and northern pike).
According to IDNR’s 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. This type of impairment, however, may not be appropriate for publicly-owned wetlands that are not managed as recreational fisheries. Regardless, this assessment segment will remain in Category 3b of Iowa’s Integrated Report.
Fish consumption uses remain "not assessed.” In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.
