Assessment Comments

Assessment is based on results of IDNR ambient quarterly water quality monitoring near Missouri Valley in 1996-1997.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed as "fully supported."  Fish consumption uses remain "not assessed."  EXPLANATION:  The assessment of support of the Class B(WW) uses was based on results of water quality monitoring during the 1996-1997 biennial period at the DNR quarterly monitoring station 2 miles east of Missouri Valley (station 822304).   For the 1998 report, the Class B(WW) aquatic life uses were assessed as "fully supported" but "threatened" due to historical impacts of extensive channelization and other impacts to the riparian corridor of the lower Boyer River (see above).   This assessment of "threatened," however, was strictly a "best professional judgement" and was not supported by field assessments of either habitat or the biological communities.   Until such assessments are conducted, the assessment of support of the Class B(WW) uses will be based only on results of the available information on chemical water quality monitoring and the comparisons of these results to the Iowa Water Quality Standards.   Thus, the assessment of support of the Class B(WW) uses was changed from "fully supported / threatened" to "fully supporting" for the 2000 report.   This assessment was based on results of quarterly monitoring.   Results from stations monitored monthly or more frequently, however, are preferred for Section 305(b) assessments in order to improve the accuracy and confidence level of the assessment.   As part of DNR's expanded water quality monitoring program, monthly monitoring at the Missouri Valley station began in October 1999.   Fish consumption uses remain "not assessed" due to the lack of fish tissue monitoring in this river reach.