ADBNet

[Note: A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and was approved by U.S. EPA in February 2013. Due to completion of the TMDL, the Integrated Report categories for the Class A1 and Class A2 recreational uses are changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved). Because not all impairments identified for this assessment segment are covered by the TMDL (aquatic life impairment due to low dissolved oxygen), this segment remains in Category 5a of Iowa's Integrated Report (impaired and TMDL required). ]

The presumptive Class A1 (primary contact recreation) and A2 (secondary contact recreation) uses remain assessed (evaluated) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2008 and 2009 at station 15030006 were as follows: the 2008 geometric mean was 218 orgs/100 ml and the 2009 geometric mean was 874 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml, and the 2009 geometric means exceed the Class A2 geometric mean criterion of 630 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, because at least one recreation season geometric mean exceeded criteria for both the presumptive Class A1 and A2 uses, these uses are assessed as “impaired.”

The results of the DNR/SHL water quality monitoring in 2009 showed no violations of the Class B(CW1) criteria for dissolved oxygen (7.0 mg/l) in the 12 samples collected from May through September. The minimum level of dissolved oxygen was 8.3 mg/l. In addition, there were no violations of pH in the 12 samples collected in 2009 nor were there violations of ammonia in the 25 samples collected in 2008 and 2009. These result suggest full support of the Class B(CW1) uses. These results are in contrast to the 2004-06 period when 42 of 80 samples violated the Class B(CW1) criterion for dissolved oxygen of 7.0 mg/l. Based on DNR's assessment methodology, however, two consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the standard are necessary to suggest de-listing of an impairment due to low dissolved oxygen. Therefore, the impairment for dissolved oxygen remained in place for the 2012 assessment/listing cycle and continues. Additional monitoring is needed to determine whether chemical water quality of this assessment segment has improved to the point where the IR 5a impairment for dissolved oxygen can be removed.

In contrast to the WQ data, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 suggests that the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Unnamed Creek (aka Bear Cr.) 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 recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population of Brown Trout at this time (a Category II stream).