Mississippi River IA 01-NEM-71

Assessment Comments

008490 (1117MBR) at Hamm Island at Dubuque, 008711 (1117MBR) downstream from Dubuque. Special study by Wisconsin DNR.

Basis for Assessment

Continue to use results of fish contaminant  monitoring conducted near Dubuque in 1994 and 1995 for the  U.S.  EPA RAFT program to assess support of the fish consumption  uses as FS.   Overall assessment changed to FST due to known  threats from point and nonpoint sources in the Upper Mississippi  River.   Also used results of special study conducted by  Wisconsin DNR (Sullivan and Endris, January 1998) that showed  low levels of dissolved oxygen (<3.0 mg/l) in the main channel  of the Mississippi River during a low flow/high temperature  period of late June/early July 1997.   Based on a study of  sediment oxygen demand in areas with and without zebra mussels,  concluded that high densities of zebra mussels, along with  decomposition of phytoplankton, are likely responsible for this  decline.   These low levels of dissolved oxygen present an  immediate threat to the water quality of the Mississippi River.