Assessment Comments
Assessment based on information from the IDNR Wildlife Bureau and results of IDNR fish kill investigations in June 2004 and July 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" based on occurrence of two fish kills in this lake during the 2003-2005 period. Historical information from the IDNR Wildlife Bureau suggests that the Class B(LW) uses should be assessed as "fully supported." The fish consumption uses remain "not assessed."
EXPLANATION: The Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment.
Information from the IDNR Wildlife Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supporting." The rationale for this assessment is as follows: the aquatic life uses of this Missouri River wetland had historically been assessed as "partially supported" since 1994 due to habitat alterations (water level instability) due to hydrologic modification (degradation) of the Missouri River channel. This wetland, however, now receives discharge water from the Port Neal Generating Station, which maintains the necessary water level in the wetland. Therefore, the impairment due to hydrologic modification is no longer applicable to this waterbody. Based on this information, the impacts from habitat alterations appear to have been adequately mitigated. Thus, the level of support of the aquatic life uses was upgraded from "partially supported" to "fully supporting" for the 2002 assessment/listing cycle.
The occurrence of two fish kills at this lake during the 2004-2007 period suggests that the Class B(LW) uses should be assessed (evaluated) as "partially supported." The first of these kills occurred on or before June 9, 2004. The kill was attributed to natural causes (“spawning stress”) related to below-normal water levels in the lake. At the time of the kill, the lake level was estimated to be approximately 18 inches below normal. The normal pumping of water into the lake from the Missouri River had been suspended for a two-week period due to high levels of turbidity and suspended solids in the river, thus adversely affecting the lake level. An estimated 200 common carp and buffalo were killed; other fish species appeared to be healthy. No estimate of the value of the fish killed was provided. The pumping of water to the lake from the Missouri River was expected to raise the lake level and help prevent additional stress to the fish populations.
The second of these kills occurred on or before July 18, 2005. The kill was attributed to natural causes (high water temperature). An estimated 65 fish were killed; all the fish were northern pike of from 3 to 15 pounds. No estimate of the value of the fish killed was provided. Because northern pike are susceptible to high water temperatures, and because other species were not affected, the kill was attributed to high water temperature (85F). Although unrelated to the kill, the lake area received 0.7-inch of rainfall the evening prior to the kill.
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 (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. Thus, this assessment segment will be placed in Category 3b of Iowa’s 2008 Integrated Report.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this wetland. In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.
