Waterloo Creek IA 01-UIA-253

The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses remain both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 26 were as follows: the 2012 geometric mean was 112 orgs/100 ml, the 2013 geometric mean was 273 orgs/100 ml and the 2014 geometric mean was 237 orgs/100 ml. The 2013 and 2014 geometric means slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Eight of the 21 samples (38%) exceeded the Class A1 single-sample maximum criterion of 235 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).

All three geometric means were well below the Class A2 geometric mean criterion of 630 orgs/100 ml, and only two of the 21 samples (9.5%) exceeded the 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, these results suggest that the Class A2 uses should be assessed as “fully supporting”. Although indicating full support, Iowa DNR’s assessment/listing methodology requires that both geometric mean criteria and single-sample maximum criteria be met for two consecutive IR cycles (five years) before a bacteria impairment can be removed. This methodology is designed to prevent impairment flip-flopping with highly variable and weather-influenced parameters such as indicator bacteria. As described in the 2014 assessment of this stream segment, the Class A2 uses were previously assessed as "impaired". Thus, the Class A2 uses will remain assessed as “impaired” for the current (2018) IR cycle.

The Class B(CW1) coldwater aquatic life uses are assessed as “fully supporting” based on results of (1) biological sampling in 2012, 2015 & 2016, (2) chemical/physical water quality monitoring conducted as part of Section 319 monitoring from April 2010 to November 2011, (3) results of chemical/physical monitoring conducted at DNR STORET station 12030012 from August 2010 to September 2011, (4) results of physical/chemical monitoring at UIRW Site 26 from 2012-2014, and (5) an DNR-Fisheries Bureau evaluation of Iowa trout streams.

The Class B(CW1) aquatic life uses were assessed (evaluated) as “fully supporting” based on biological data collected in 2012 and 2016 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 2012 CBI scores were 49, 75 and 90. The 2015 and 2016 CBI scores were 76 and 51. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 3/5 times in the last five years (2012-2016). 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 over a five-year period to be considered “monitored”.

Results of Section 319 chemical/physical water quality monitoring in 2011 also suggest “full support” of the Class B(CW1) aquatic life uses of this stream segment. Seven samplings were conducted in 2011 at the three monitoring stations in this segment (Waterloo Creek sites 1, 2, and 5). Results of monitoring for dissolved oxygen show that two of the combined 21 samples violated the Class B(CW1) criterion for temperature of 7 mg/l (9.5% violation). The two violations of the Class B(CW1) dissolved oxygen criteria occurred at Waterloo Creek Station 5 and were 6.7 mg/l on August 24, 2011 and 6.6 mg/l on September 6, 2011. According to the DNR assessment methodology, if the percentage of sample that violate water quality criteria for conventional parameters such as dissolved oxygen is less than 10%, the aquatic life uses should be assessed as “fully supported”. Additional monitoring for dissolved oxygen, pH, and ammonia was conducted at STORET Station 12030012. None of the nine samples collected between August 2010 and September 2011 violated the Class A2 criterion for either of these parameters. Monitoring at the three 319 stations and at station 12030012 show no violations of the Class A2 criterion for water temperature (20C) in the combined 42 samples collected from August 2010 to November 2011. Results of water quality monitoring at Site 26 of the Upper Iowa River Watershed (UIRW) project also suggest “full support” of the Class B(CW1) uses. Monitoring from 2012 to 2014 at this monitoring station included analysis of 14 samples for ammonia, temperature, and pH. None of these samples collected violated the respective Class B(CW1) criteria.

In addition, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019, also suggests the Class B(CW1) uses are "fully supported". According to the updated summary, Waterloo 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). This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.

Taken together, the results of biological, chemical/physical water quality monitoring, and trout stream evaluation all suggest that that Class B(CW1) aquatic life uses of this stream segment should be assessed as “fully supporting”.

Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment.