Des Moines River IA 04-LDM-1010

Sources of Data:

Class A1 - Indicator Bacteria:

Class A1 - pH:

Class BWW1 - Conventional Parameters:

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

Overall:

Class BWW1 – Fishkill Assessment:

The Class BWW1 aquatic life use remains assessed as “partially supported” due to fish kills on July 10, 2006, and on July 7, 2012 on the reach of river between Eldon (Wapello Co.) and Douds (Van Buren Co.). These kills are in a series of kills that have occurred over the last 15 years or so that appear to involve primarily shovelnose sturgeon (Scaphirhynchus platorynchus). Although the cause of the three recent kills and the previous kills remains unknown, the leading hypotheses are (1) that very high water temperatures, very low river flows, and elevated pH levels combine to make ambient levels of ammonia in the river toxic to the ammonia-intolerant shovelnose sturgeon and (2) that the kills are caused by a virus specific to shovelnose sturgeon. The most recent kill in July 2012 was especially severe. According to the local DNR Fisheries biologist, the kill was reported on the lower Des Moines River on July 7, 2012, from approximately Eldon (downriver from Ottumwa) to Farmington in Van Buren County. An estimated 57,000 fish were killed including at least 35,000 shovelnose sturgeon. No specific cause of the kill was identified, but low flow conditions, flow alterations, and very high water temperatures (95+F) are believed to have contributed to the kill.

According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates that the aquatic life uses of a waterbody are only "partially supported.” Thus, the Class BWW1 aquatic life uses of this river reach were assessed as "partially supported” (303(d) impaired). Also, according to DNR’s assessment methodology, if a cause of a fishkill was not identified during the DNR investigation (cause = "unknown"), 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, typically lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (Category 5 of the Integrated Report). Waterbodies affected by such fish kills at usually placed in IR subcategories 2b or 3b and are added to the state’s list of “waters in need of further investigation”. Due however to (1) the repeated occurrence of these kills over the last 15 years in Wapello and Van Buren counties, (2) the large numbers of sturgeon killed (thousands), (3) the likelihood that these kills are caused by a pollutant and (4) the possibility that the kills have extended further downstream (possibly to Bonaparte), this impairment was added to Iowa’s 2008 Section 303(d) list (Category 5 of the Integrated Report).

Class HH – Fish Tissue Sampling: