Wapsipinicon River IA 01-WPS-6416

A fish kill that originated in Minnesota occurred on this stream on April 28, 2016. A Mitchell County LEO, relayed information he received about the fish kill that occurred in the coldwater section of the Wapsipinicon River likely sometime April 28 following several bouts of rain showers earlier in the week. Approximately 6.3 miles of stream were affected, 420 fish were killed valued at $37.80.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 three-year period (2014-2016) 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, either are inappropriate for state Section 303(d) listing (no pollutant load to allocate) or lack the degree of confidence to support addition to the state’s Section 303(d) list of impaired waters. Waterbodies affected by such fish kills will be placed in IR Category 3b and will be added to the state list of waters in need of further investigation.

The evaluated biological assessment of the presumptive Class B(WW1) aquatic life uses was historically based on data collected in 2010 as part of the DNR/SHL headwater stream IBI development project. A series of biological metrics that 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 collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The BMIBI score was 65 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the BMIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The natural substrate BMIBI BIC for this ecoregion is 70. Even though this site passed the BMIBI BIC (using the BMIBI UAV of 8 points), 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.