Bear Creek IA 01-MAQ-34

The assessment of the Class B(WW2) aquatic life uses is based on data collected in 2011 and 2015 as part of the DNR/SHL stream biocriteria project. 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 2011 FIBI score was 73 (excellent) and the 2011 BMIBI score was 69 (good). The 2015 FIBI score was 71 (excellent) and the 2011 BMIBI score was 63 (good).The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 2/2 times in the last six years.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years in the most recentfive-year period to be considered “monitored”. This segment had multiple samples collected in the previous six years; however, multiple samples were not collected during the recent five-year period.

From the 2008 IR cycle until this cycle (2018), the assessment of the Class B(WW2) aquatic life uses was based on the occurrence of a fish kill in 2007 that suggested that the aquatic life uses should be assessed (evaluated) as "partially supported."The kill occurred on or before August 21, 2007; no cause was identified for this fish kill. Approximately 3,497 fish were killed on August 21 and 22, 2007. The kill affected 5 miles of the stream from 2 miles south of Monmouth to the south edge of Baldwin. The estimated value of the fish was $11,145.37.

According to DNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill was not identified during the DNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. According to Iowa DNR’s assessment/listing methodology, any IR 2b or 3b fish kills that occurred more than 10 years ago will be moved to IR Category 3a (not assessed) for the current (2018) IR cycle.