Trout Creek (aka Trout Run) IA 01-UIA-269

The Class A3 (children’s contact recreation) uses and the Class A2 (secondary contact recreation) uses remain assessed (monitored) as “not supported” (impaired) due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 16 were as follows: the 2012 geometric mean was 211 orgs/100 ml, the 2013 geometric mean was 957 orgs/100 ml and the 2014 geometric mean was 2,034 orgs/100 ml. All three geometric means exceed the Class A3 criterion of 126 orgs/100 ml; the 2013 and 2014 geometric means exceed the Class A2 geometric mean criterion of 630 orgs/100 ml. Fifteen of the 21 samples (71%) exceeded the Class A3 single-sample maximum criterion of 235 orgs/100 ml; six of the 21 samples (29%) exceeded the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as impaired (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, both the Class A3 and Class A2 uses should be assessed as “not supporting”.

The Class B(CW1) aquatic life uses are assessed (monitored) as “partially supporting” based on biological data collected in 2013 and 2014 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 2013 CBI scores were 44 and 53. The 2014 CBI scores were 38 and 61. The aquatic life use support was assessed (monitored) as partially 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 1/4 times in the last five years.

This aquatic life assessment is now considered "monitored" 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 previous five years.

In contrast to the benthic macroinvertebrate sampling, 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, Trout Creek (aka Trout Run) is in the group of Iowa coldwater streams that support 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 consistent natural reproduction and maintain a wild population of brown trout without any stocking (Category I stream).

Results of water quality monitoring from 2012 to 2014 at Upper Iowa River Watershed Site 19 suggest that the Class B(CW1) coldwater aquatic life uses should be assessed as “fully supported”. This monitoring included analysis for ammonia, pH, and temperature. Of the 14 samples analyzed for ammonia, 13 samples contained less than the limit of detection (0.05 mg/l); the one sample with a detectable level of ammonia contained 0.27 mg/l of ammonia. This level is far below the temperature/pH-dependent chronic criterion for ammonia of 2.4 mg/l. In addition, none of the 14 samples contained levels of pH or temperature that violated Class B(CW1) criteria. Thus, these results do not suggest impairment of the Class B(CW1) aquatic life uses.

Results of continuous dissolved oxygen (DO) and temperature monitoring in 2013 and 2014 for the DNR/SHL coldwater stream sampling projects also suggest Class B(CW1) aquatic life uses are fully supported. The lowest DO concentration recorded in 75 days of continuous monitoring was 8.3 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 75 days each. The percentages 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 21.6 degrees (C). The B(CW1) temperature criterion of 20 (C) was exceeded in 1 of 75 days. The percentage exceeding (1.3%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(CW1) aquatic life use is assessed as not impaired by DO and temperature. The assessment type is “monitored” because the data meet the minumum requirements of the DNR’s continuous monitoring assessment methodology.

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.