Dry Creek IA 06-BSR-1878

Results of stream REMAP biological sampling in 2004-2006 suggest that the presumptive Class B(WW1) aquatic life uses of this stream segment should be assessed (evaluated) as "partially supported". This assessment was based on biological data collected in 2004-2006 as part of the DNR/SHL stream REMAP project. A series of biological metrics that reflect 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 and fish species 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 2004 FIBI score was 0 (poor) and the BMIBI score was 28 (poor). The 2005 FIBI score was 0 (poor) and the BMIBI score was 40 (fair). The 2006 FIBI score was 0 and the BMIBI score was 42 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 0/3 times and passed the BMIBI BIC 0/3 times in the last nine years. Even though this site failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size. Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).

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). However, despite this change in assessment methodology and type, this waterbody was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters.

Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. DNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality. Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams.

In addition to results of biological monitoring that suggest impairment, the occurrence of a fish kill in September 2003 also suggests impairment of the aquatic life uses of this stream. This kill occurred on or before September 13, 2003; the kill was attributed to low levels of dissolved oxygen in a oxbow/backwater of Dry Creek. An estimated 1,501 fish were killed. According to the fish kill report; all fish were common carp except one crappie. No estimated value of the fish killed was provided. No estimate was provided for the size of the waterbody affected by the kill. The kill occurred in a backwater of Dry Creek at the southwest edge of Hawarden, IA; the location point for the kill is the NW1/4 of the SW1/4 of Section 2, T94N, R48W, Sioux County. According to the DNR investigation, dead fish were concentrated in a small backwater oxbow. Heavy rains in the area on September 13 may have allowed the carp to move into backwaters and oxbow; when stream level dropped the fish were trapped in the oxbow with no oxygen or water. A reporter noticed a muddy smell on 9/14 and noticed that fish were dying. During the investigation, oxygen levels were greater than 15 ppm and ammonia levels ranged from 1.0 to 1.5 ppm. The water was clear to mud stained. The kill was attributed to natural causes. This kill and others that occurred in smaller streams in northwest Iowa from September 11-15, 2003 were believed related to a rainfall event or events that followed a prolonged dry period. None of the investigations of these kills, however, suggested a specific pollutant-related cause.

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”. Because the 2003 fish kill on this stream resulted in addition of this segment to Category 5b of Iowa's 2006 Integrated Report, this segment remains in Category 5b of Iowa's Integrated Report.