Unnamed Tributary to Ralston Creek IA 02-IOW-6300
from mouth (SW1/4 S11 T79N R06W Johnson Co.) to headwaters in NE1/4 S7 T79N R05W Johnson Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 7/22/2019 12:14:14 PM
- Updated
- 7/22/2019 12:15:42 PM
The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses are assessed as "partially supported" based on results of a fish kill investigation in May 2009.
A fish kill occurred on or before May 24, 2009. The kill affected hundreds of fish along approximately a mile-and-a-half long stretch of this tributary of Ralston Creek. The creek was traced back to a tile line in a rural area, but there was no indication of manure or fertilizer run-off based on field testing. Analyses of water samples were inconclusive, and no cause could be determined.
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). ). Due, however, to the large number of fish killed ("hundreds"), the length of the kill (1.5 miles), and the lack of environmental extremes during spring 2009 that would have contributed to this kill (e.g., low stream flow and/or high water temperatures), some type of pollutant cause is suspected. Thus, this assessment was moved from Category 3b of Iowa's 2010 Integrated Report (potentially impaired) to IR Category 5b (impaired) of the 2012 IR. This impairment remains in IR Category 5b.