Cedar Creek IA 04-LDM-1054

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) 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 now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

This evaluated biological assessment was based on data collected in 2006 and 2014 as part of the IDNR/SHL stream sampling projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2006 FIBI score was 1 (poor) and the BMIBI score was 32 (fair).  The 2014 FIBI score was 21 (poor) and the BMIBI score was 47 (fair).  The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.  This segment passed the FIBI BIC 0/2 times and passed the BMIBI BIC 1/2 times in the last nine years.

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a recent five-year period.  This segment had multiple samples; however, they were collected in a nine year period (2006-2014) and not in the most recent five year period (2010-2014).  According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).

In addition to the low IBI scores, dead and rotten fish were observed in the sampling reach during the 2006 sampling. Sampling staff estimated that a fishkill of unknown origin and magnitude had occurred within the week prior to sampling; however, this kill was never officially reported or investigated. This unreported kill represents a potential impairment of the Class B(WW2) aquatic life uses. While not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5), this potential impairment is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation.