Bear Creek IA 06-LSR-1833

The presumptive Class B(WW1) aquatic life uses remain assessed as “partially supported” (IR 3b) due to a fish kill that occurred on or before September 28, 2015, 4 miles NW of Meriden at K and L avenue bridges. The following are notes from the fish kill investigation:

FO3 received a page early on Saturday morning from a chub fisherman near Meriden in Cherokee County. He said there were “hundreds” of dead chubs and minnows under a bridge north of Meriden in Bear Creek. Bear Creek flows northeasterly from that point about one mile and discharges into Mill Creek. Water quality parameters were normal with high DO and low ammonia. Dead fish were only observed under two bridges. The second bridge, on C16 right before Bear Creek enters Mill Creek, had a few floaters that appeared to come from a pooled area under the bridge at L Avenue where most of the dead fish were observed, just south of County Road C16. Flows in the creeks were high from rains in the area over the past few weeks. No dying fish were observed. This area had received approximately 1 inch of rain during the previous two days. We contacted two cattle facilities in the area but saw no evidence of runoff. It is possible some pollutants entered the stream and were washed away by the time we responded. Fisheries personnel did not conduct a count as no obvious source was determined. It is also possible that DO levels dropped in the pooled water overnight, killing fish, and then returned to normal. It is also possible that the fish died of “natural” causes.

No estimates were provided for the number of fish killed, the value of the fish killed, or the cost of the Iowa DNR investigation. The kill affected approximately 1 mile of stream.

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 (2012-2016) 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.

The assessment of the presumptive Class B(WW1) aquatic life uses was also based on data collected in 2002 as part of the DNR/SHL stream REMAP 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 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). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 FIBI score was 36 (fair). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score 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. Even though this site passed the FIBI BIC (using the FIBI uncertainty adjustment value of 7 points applied to single samples), 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. Additionally, 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).