South Fork Iowa River IA 02-IOW-746

Assessment Comments

Assessment is based on results of (1) USGS/NAWQA monitoring of water quality (1998-2001) and (2) occurrence of fish kills in the watershed.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed as "fully supported / threatened;" the fish consumption uses remain assessed as "fully supported."  EXPLANATION:  The assessment of support of the Class B(WW) uses for the 2000 report is based (1) on results of monitoring conducted on South Fork Iowa River near New Providence from March 1996 to August 1998 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05451210) and (2) on the history of fish kills in this watershed (see above).   The USGS / NAWQA  monitoring showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the 38 samples collected and (2) no violations of the Class B(WW) chronic water quality criterion for pesticides in the 22 samples analyzed.   Although no fish kills were reported for this reach of the South Fork Iowa River during October 1997-September 1999 biennial period, fish kills continue to occur in this watershed (for example, a fish kill was reported for Tipton Creek in July 1998).   In addition, this river reach appears to have elevated levels of nutrients.   The mean level of total phosphorus over the March 1996-August 1998 USGS monitoring period was 0.30 mg/l (N=38; SE=0.07 mg/l) with five samples during this period containing over 1.0 mg/l of total phosphorus (maximum = 1.6 mg/l).   Thus, based on the results of USGS/NAWQA monitoring and the history of fish kills in this watershed, the Class B(WW) aquatic life uses were assessed as "fully supported / threatened."  Fish consumption uses remain assessed as "fully supported" based on results of the USGS/NAWQA fish tissue monitoring in September 1995 that showed levels of organochlorine contaminants were less than ½ of the respective FDA action levels and DNR levels of concern (see assessment for the 1998 report).