Cedar River IA 02-CED-474

Assessment Comments

Assessment is based on results of a fish kill investigation in July 2006.

Basis for Assessment

SUMMARY: 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 are assessed (evaluated) as "partially supported" due to a fish kill in July 2006.   The fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring in this segment.   The assessment is based on results of a fish kill investigation on July 12, 2006.  

EXPLANATION: 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 are 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.

According to IDNR’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 (2004-2007) 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.”  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.   Thus, this assessment segment will be placed in Category 3b of Iowa’s 2008 Integrated Report.

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