Cedar River IA 02-CED-474

The Class A1 (primary contact recreation) uses remain "not assessed" due to a lack of information upon which to base an assessment. 

The Class B(WW1) (aquatic life) uses remain assessed (evaluated) as "partially supporting" based on results of a fish kill investigation in July 2006.  The kill occurred on or before July 12, 2006 and was attributed to natural causes.  The dead fish were located in a backwater area, not the Cedar River itself.  It was noted that when river levels are high fish have access to these backwater areas, but when river levels go down the backwater is isolated from the river, trapping fish there.  The kill was likely caused by low dissolved oxygen in the backwater area.  It was noted that this area is covered with aquatic vegetation, which causes changes in dissolved oxygen levels in the pool.  The dissolved oxygen concentration on the morning of July 12, 2006 was 2 ppb.  An estimated 100 fish were killed in this pool.  No estimate of the value of these fish was made. 

This is the same assessment as that developed for the previous assessment/listing cycles.  The continuance of the IR Category 3b listing is based on IDNR's assessment methodology that states the following:  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 IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.  Thus, this assessment segment will remain in Category 3b of Iowa’s Integrated Report. 

In contrast to the assessment based on the fishkill in this segment, the evaluated biological assessment based on data collected in 2009 as part of the IDNR Fisheries sampling project suggests "full support" of the aquatic life uses.  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 fish species 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 2009 FIBI score was 57 (good). 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 biological data collected at stream ecoregion reference sites from 1994-2008.  The non-riffle habitat FIBI BIC for this ecoregion is 44.  This assessment is considered evaluated because the drainage area (1465 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.  Even though this site passed the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size.

The fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring in this segment.