Little Rock River IA 06-BSR-1798

Assessment Comments

Assessment is based on results of (1) biological monitoring conducted by IDNR Fisheries in 2000: Fish IBI = 62 (good) and (2) IDNR/UHL ambient water quality monitoring conducted in 2002 in support of TMDL development.

Basis for Assessment

[NOTE:  For the 2002 report, the previous waterbody segment for Little Rock River (IA 06-BSR-0060-0), which extended 46 miles from its mouth in Lyon County to the Iowa/Minnesota state line, was split into three subsegments:  (1) (this one) from mouth to Otter Creek near George (IA 06-BSR-0060-1), (2) Otter Creek to Argo Slough near Little Rock (IA 06-BSR-0060-2), and (3) Argo Slough to the Iowa Minnesota state line (IA 06-BSR-0060-3).   See assessment information found in subsegment IA 06-BSR-0060-2 for previous Section 305(b) assessments for the entire 46-mile reach.]

SUMMARY:  SUMMARY:  The Class B(LR) aquatic life uses are assessed (evaluated) as “fully supported” based on (1) results of biological monitoring for fish conducted in 2002 by the IDNR Fisheries Bureau and (2) results of IDNR/UHL ambient water quality monitoring conducted in 2002 as part of TMDL monitoring (TMDL station 6; STORET station 11600005).

EXPLANATION:  This assessment was based on data collected in 2000 as part of a DNR Fisheries stream sampling project: Manchester research station.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (F-IBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2000 evaluated Fish IBI was 62 (good).   The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.

Similarly, results of chemical/physical water quality monitoring conducted from March through November 2002 by IDNR/UHL in support of TMDL development suggest relatively good water quality in this stream.   None of the 10 samples collected had levels of dissolved oxygen, pH, or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides).   The decision to consider this assessment as “evaluated” (lower confidence) versus “monitored” (higher confidence) is based on (1) the relatively few samples collected (10) and the relatively poor parameter coverage (i.e., no analysis of samples for toxic metals or pesticides).