Assessment Comments
Assessment is based on results of (1) IDNR/UHL ambient monthly monitoring near Hornick from 2002-04.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment for the West Fork Little Sioux River (IA 06-LSR-0120-0), which extended 32 miles from its mouth to confluence with Mud Creek near Moville in Woodbury Co., was split into two subsegments: (1) mouth to confluence with an unnamed tributary 0.5 miles north of Climbing Hill (Woodbury Co. - this one) (IA 06-LSR-0120-1) and (2) unnamed tributary 0.5 miles north of Climbing Hill to Mud Creek near Moville, Woodbury Co. (IA 06-LSR-0120-2). See previous Section 305(b) from this subsegment for the assessments of the original 32-mile river reach.]
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as "fully supported" based on results of IDNR/UHL ambient water quality monitoring from 2002 through 2004. The extensive channel modifications on this river segment, however, remain a concern regarding the full support of aquatic life uses. This assessment is based on (1) results of IDNR/UHL monthly ambient monitoring conducted during the 2000-2002 assessment period on West Fork Little Sioux River at the Highway 141 bridge approximately 1 mile east of Hornick in (STORET station 10970002).
EXPLANATION: Monitoring at the IDNR station east of Hornick showed no violations of Class B(LR) water quality criteria in the 36 samples collected during the 2002-2004 assessment period for dissolved oxygen (minimum value = 7.6 mg/l), pH (range = 7.9 to 8.8 units), or ammonia-nitrogen (maximum value = 1.1). Levels of pesticides in the 11 samples analyzed were all below the analytical level of detection. None of the 10 samples analyzed for toxic metals during the assessment period exceeded the respective Class B(LR) criteria. These results suggest "full support" of the Class B(LR) aquatic life uses. The extensive habitat alterations due to channel straightening in this stream system suggest a concern regarding full support of the aquatic life uses. This conclusion is based on a stream use assessment conducted by IDNR staff in 1995 (see assessments developed for the 1996, 1998, and 2000 reporting cycles for more information).
