Sny Magill Creek IA 01-YEL-430

Assessment Comments

Assessment remains based on a February 2011 DNR summary of trout reproduction. Other data include results of historical monitoring at Sny Magill project sites.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses and presumptive Class A2 (secondary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of data for indicator bacteria upon which to base an assessment.   The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a).   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this coldwater stream.   Sources of data for this assessment include (1) a summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011 and (2) results of water quality monitoring conducted from January 2000 through September 2001 at three sites on Sny Magill Creek:  Site 1 (IDNR station 15220004), Site 2 (IDNR station 15220005), Site 3 (IDNR station 15220002).  

EXPLANATION:  The Class B(CW1) uses remain assessed as "fully supported" based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011.   According to the updated summary, Sny Magill Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout.   In previous IDNR summaries of trout reproduction, this stream was placed in the category of Iowa trout streams that have fairly consistent natural reproduction and that are capable of maintaining a viable population for the target trout species without any stocking.   Based on results of surveys by the IDNR Fisheries Bureau, however, this stream is now placed in the category of Iowa trout streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the resident trout species at this time.   Although still considered “fully supporting”, this assessment based on the 2011 summary of trout reproduction reflects a decline in the ability of this stream to support natural reproduction of trout.  

Monitoring of chemical water quality, habitat quality, fish populations, and aquatic macroinvertebrate populations was conducted at Sny Magill Creek from 1992 to the early 2000's as part of the Sny Magill Creek Nonpoint Source Pollution Monitoring Project.   Results of this monitoring showed good chemical water quality and aquatic life.   The assessment of aquatic life uses in this stream segment as "fully supported" was based on results of chemical and biological water quality monitoring conducted from 1992 through 2001 at three monitoring sites (see previous assessments).   Of the approximately 200 samples analyzed at these stations during 2000-01, no samples violated the respective Class B(CW) water quality criteria for dissolved oxygen and temperature.   All these data, however, have aged well beyond the ten-year period during which water quality data is considered able to characterize current water quality conditions.   Thus, the results of the monitoring from 1999-2001 may have little relevance to current water quality conditions in this assessment segment.

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.