Winnebago River IA 02-WIN-826

Assessment Comments

Assessment is based on results of (1) IDNR/UHL monthly ambient city monitoring downstream form Mason City from 2000-02, (2) U.S. EPA/IDNR fish contaminant monitoring in 1998, and (3) two water quality studies conducted for Lehigh Cement Co. in 1994-95.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses remain assessed (evaluated) as "fully supported / threatened" based on results of biological monitoring conducted as part of water quality studies in 1994 and 1995.   Fish consumption uses remain assessed as "fully supported" based on results of fish contaminant monitoring in 1998.   The sources of data for this assessment include (1) results of monthly monitoring from May 2000 through December 2002 at the IDNR ambient city monitoring station located downstream from Mason City (STORET station 10170003) and (2) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 1998.   The assessment is also based, in part, on water quality studies conducted in 1994 and 1995 for the Lehigh Portland Cement Company.  

EXPLANATION: The results of IDNR/UHL water quality monitoring downstream from Mason City (STORET station 10170003) suggest “full support of the Class B(WW) aquatic life uses.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 28 samples collected, or for pesticides in the nine samples collected during the 2000-2002 assessment period.   Only one of the 28 samples collected contained total dissolved solids (TDS) above the general use standards on 750 mg/l (the sample collected on July 2, 2001 contained 1,640 mg/l of TDS).   Although these results suggest "full support" of the Class B(WW) aquatic life uses, the results of the water quality studies conducted in 1994 and 1995, which show relatively low diversity of the fish community downstream from Mason City, continue to suggest the possibility of threats to full support of the aquatic life uses.   Follow-up  monitoring is needed to better determine the status of the aquatic communities of this reach of the Winnebago River and to determine whether the Class B(WW) uses may be impaired.   Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 1998 (see assessment for the 2000 report).