Tetes Des Morts Creek IA 01-TRK-121

The Class A1 and A2 uses remain assessed (monitored) as “not supported" due to levels of indicator bacteria (E. coli) that exceed the respective Class A1 and A2 geometric mean criteria. The geometric mean of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2010 and 2011 at the Section 319 monitoring station Tetes Des Morts Site 3 were 713 and 106 orgs/100 ml, respectively. The geometric mean of indicator bacteria (E. coli) in the 24 samples collected during these recreational seasons at Tetes Des Morts Site 2 were 1,578 and 822 orgs/100 ml, respectively. Three of the four recreation season geometric means exceed Iowa’s Class A1 geometric mean criterion of 126 E. coli orgs/100 ml and, three of four also exceed the Class A2 geometric mean criterion of 630 E. coli orgs/100 ml, thus indicating nonsupport of both the Class A1 and A2 water contact recreation uses. Eight of the 21 samples (37%) at Site 3 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, and 20 of 24 samples (83%) exceeded this criterion at Site 2. The percentages of violations of the Class A2 single-sample maximum criterion (2,880 orgs/100 ml) were much lower with 2 of 21 samples (10%) exceeding this criterion at Site 3 and five of 24 samples (21%) exceeded this criterion at Site 2. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1 and 630 orgs/100 ml for Class A2), the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). In addition, the percentage of samples with levels of E. coli that exceeded Iowa single-sample maximum criteria indicate impairment of the contact recreation uses for both Class A1 and A2 uses at both monitoring sites.

Regarding the Class B(WW1) aquatic life uses, this assessment, in part, was based on data collected in 2011, 2014 and 2016 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 biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 70 (good) and the BMIBI score was 59 (good). The 2014 FIBI score was 74 (excellent) and the BMIBI score was 54 (fair).The 2016 FIBI score was 67 (good) and the BMIBI score was 66 (good). 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 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 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 1/3 times in the last six years (2011-2016).

Water quality data were collected from April to October of 2011 at the Section 319 project sites: Site 2 at the Highway 52 bridge (STORET station 12490004) and Site 3 at the High Road Bridge (STORET station 13490002). The results of this monitoring do not suggest impairment of the Class B(WW1) aquatic life uses. Two of the 11 samples collected at Site 2 violated the Class B(WW1) criterion for dissolved oxygen of 5 mg/l: the sample collected on August 8th contained 4.9 mg/l and the sample collected on July 19th contained 4.5 mg/l. At Site 3, one of the 11 samples violated the dissolved oxygen criterion: the sample collected on July 11th contained 2.6 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to DNR’s assessment/listing methodology, however, the results from these two stations on Tetes des Morts however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for dissolved oxygen. Thus, these results suggest that the Class B(WW1) uses should be assessed (evaluated) as “fully supported.”

Despite the results of chemical monitoring that suggest good water quality in Tetes des Morts Creek (i.e., "full support" of the Class B(WW1) uses), the results of biological monitoring suggest an impairment ("partial support") of the aquatic life uses. Because stream biota (fish and aquatic macroinvertebrates) integrate water quality impacts over the long-term, the results of biological monitoring are typically weighted more than results of chemical monitoring when determining support of aquatic life uses for purposes of Section 305(b) reporting. This approach is consistent with recommendations in U.S. EPA's guidelines for Section 305(b) reporting (see U.S. EPA 1997b, page 3-21). Thus, considering the "full support" suggested by results of chemical monitoring, and the "partial support" suggested by results of biological monitoring, the aquatic life use of this segment of this stream remain assessed as "partially supported."

The occurrence of a fish kill in August 2005 historically suggested only "partial support" of the Class B(WW1) aquatic life uses of this stream. This kill occurred on or before August 18, 2005; no cause of the kill was identified. An estimated 3,363 fish were killed with value of $11,914.36. Game fish killed included channel catfish (53), flathead catfish (18), smallmouth bass (370), and walleye (141). The kill affected approximately two miles of stream. No responsible party was identified. Because no cause, source or responsible party was identified, this fishkill should have been put in Category 3b (assessment error). 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. In addition, there have been eight (8) fish community index of biotic integrity (FIBI) samples collected in this segment since the fishkill. Seven of the eight scores (7/8) passed the FIBI BIC for this ecoregion (52). In the opinion of Iowa DNR, any fish related impairment in this segment related to the 2005 fishkill no longer exists (the 5b-v impairment in this segment is because of slightly low BMIBI scores).

Class HH (fish consumption) uses are assessed as "fully supported" based on results of DNR fish tissue monitoring near St. Donatus in 2016. The average level of mercury in the tissue plugs from three smallmouth bass in 2016 was 0.143 ppm (SD=0.032).The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the tissue samples from fish collected at St. Donatus do not exceed any of Iowa’s consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.