Twin Springs Creek (aka Spring Falls) IA 01-TRK-181

Assessment Comments

Assessment is based on 2007 IDNR/UHL biological monitoring data and on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006.

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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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" due to the lack of data for indicator bacteria upon which to base an assessment.   The Class B(CW1) coldwater aquatic life uses are assessed (monitored) as "fully supported" based on 2007 IDNR/UHL benthic macroinvertebrate sampling and on the May 2006 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.    Fish consumption uses remain "not assessed."  

EXPLANATION:  Based on an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in May 2006, the Class B(CW1) uses are assessed as "fully supported".    According to the updated summary, Twin Springs Creek (aka Spring Falls) is in the group of Iowa coldwater streams that supports natural reproduction of trout.   Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking.  

This assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007 as part of the IDNR/UHL coldwater stream sampling project.   A series of four (4) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the benthic macroinvertebrate sampling data.   The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa that were collected the stream sampling reach.   Sites where only a benthic macroinvertebrate sample was obtained or sites that do not receive any type of trout stocking are scored on the benthic macroinvertebrate data only.   Non-trout stocking sites that score 3 or 4 are fully supporting (FS), sites that score 1 or 2 are partially supporting (PS), and sites that score 0 are not supporting (NS).   The 2007 coldwater biological indicator score was 3/4.   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the coldwater biological indicator score with biological assessment criteria established for this Section 305(b) report.   The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2008 and with assistance from the IDNR Fisheries Bureau.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”.   This segment had a single sample collected in 2007.   Despite this change in assessment methodology and type, this waterbody was placed in IR Category 2a.

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