Clear Creek IA 01-UIA-235

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007 and 2013 as part of the DNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 CBI score was 68. The 2013 CBI scores were 48 and 49. The aquatic life use support was assessed (evaluated) aspartially supporting (=PS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.The CW BIC is 60 and this segment passed the CW BIC 1/3 times from 2007-2013.

This aquatic life assessment is 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 a recent five-year period to be considered “monitored”. This segment had multiple samples collected in the last 11 years. According to DNR’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). DNR 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).

In contrast to the benthic macroinvertebrate data, the updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019, suggests the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Clear Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the DNR 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 brown trout without any stocking (Category I stream).

The results of continuous dissolved oxygen (DO) and temperature monitoring in 2013 for the DNR/SHL coldwater stream sampling project also did not suggest impairment of Class B(CW1) uses. The lowest DO concentration recorded in 71 days of continuous monitoring was 7.0 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (5 mg/L) and the 16-hour DO criterion (7 mg/L) in 0 of 71 days each. The percentage exceeding (0%) was less than (passing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level was high (>90%). The maximum stream temperature recorded during the sensor deployment period was 20.9 degrees (C). The B(CW1) temperature criterion of 20 (C) was exceeded in 5 of 71 days. The percentage exceeding (7%) was less than (passing) the 10% impairment threshold; however, the statistical analysis confidence level (< 90%) was not high. Based on these data, the B(CW1) aquatic life use is assessed as fully supporting with respect to DO and temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the DNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.

The Class A1 (primary contact recreation) uses, Class A2 (secondary contact recreation) uses and Class HH (fish consumption) uses remain "not assessed" due to the lack of information upon which to base an assessment.