Decatur Lake IA 06-WEM-1727

Assessment Comments

Assessment remains based on (1) information from the IDNR Wildlife Bureau and (2) results of watershed modeling by the IDNR Water Quality Bureau.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.   The Class B(LW) aquatic life uses remain assessed (evaluated) as "not supported" based on information from the IDNR Wildlife Bureau.   This assessment was also based on results of watershed modeling conducted by IDNR staff in 2002.   Fish consumption uses remain "not assessed."  This assessment is the same as that developed for the 2002 and 2004 assessment/listing cycles.  

EXPLANATION:  The Class A (primary contact recreation) uses remain "not assessed" due to a lack of water quality information upon which to base an assessment.   In general, Iowa wetlands are not managed to support primary contact recreation.

The Class B(LW) aquatic life uses remain assessed as "not supported" based on information from the Iowa DNR Wildife Bureau (see assessments developed for the 1998 and 2000 reporting cycles).   Decatur Lake is part of an Army Corps of Engineers mitigation project along the Missouri River; this project will result in water being pumped into the wetland thus correcting the flow alteration impairment.   Watershed modeling completed in 2002 for Decatur Lake indicates that sediment delivery to this wetland from the watershed is very low.   The local DNR biologist indicates that the Missouri River does not breach the original high bank, but occasionally (10 -15 years) flood waters do enter the wetlands directly adjacent to the river.   Based on the watershed modeling data, the wetland is no longer considered "impaired" by siltation from agricultural nonpoint sources.   An updated assessment for this wetland will be needed following completion of the mitigation project.   The assessment category for this wetland of "evaluated" indicates that the assessment is based entirely on "best professional judgement."  In terms of Section 305(b) reporting, "monitored assessments" are based primarily on recent, site-specific ambient monitoring data and thus have relatively high confidence.   IDNR considers waterbodies identified as "impaired" based on "monitored assessments" as candidates for the state's Section 303(d) list.   "Evaluated assessments" are those based on data older than five years or other than site-specific ambient monitoring data (e.g., questionnaire surveys of fish and game biologists [=best professional judgement]) and thus have relatively low confidence.   IDNR does not consider waterbodies identified as "impaired" based on "evaluated assessments" as candidates for the state's Section 303(d) list.    

Fish consumption uses remain "not assessed."  In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.