characteristics for a sufficient portion of the growing season 

 to qualify as a wetland under the Clean Water Act must be made 

 on a case-by-case basis. Such determinations should consider 

 the respective length of time that the area exhibits upland and 

 wetland characteristics, and the manner in which the area fits 

 into the overall ecological system as a wetland. Evidence con- 

 cerning the persistence of an area's wetness can be obtained 

 from its history, vegetation, soil, drainage characteristics, 

 uses to which it has been subjected, and weather or hydrologic 

 records. 



c. Prairie potholes. Prairie potholes normally occur as shallow 

 depressions in glaciated portions of the north-central United 

 States. Many are landlocked, while others have a drainage out- 

 let to streams or other potholes. Most have standing water for 

 much of the growing season in years of normal or above normal 

 precipitation, but are neither inundated nor have saturated 

 soils during most of the growing season in years of below nor- 

 mal precipitation. During dry years, potholes often become 

 incorporated into farming plans, and are either planted to row 

 crops (e.g. soybeans) or are mowed as part of a haying opera- 

 tion. When this occurs, wetland indicators of one or more 

 parameters may be lacking. For example, tillage would elimi- 

 nate any onsite hydrologic indicator, and would make detection 

 of soil and vegetation indicators much more difficult. 



d. Vegetated flats. In both coastal and interior areas throughout 

 the Nation, vegetated flats are often dominated by annual spe- 

 cies that are categorized as OBL. Application of procedures 

 described in Sections D and E during the growing season will 

 clearly result in a positive wetland determination. However, 

 these areas will appear to be unvegetated mudflats when exam- 

 ined during the nongrowing season, and the area would not 

 qualify at that time as a wetland due to an apparent lack of 

 vegetation. 



Wetland determi- 

 nations in problem areas 



79. Procedures for making wetland determinations in problem areas are 

 presented below. Application of these procedures is appropriate only when a 

 decision has been made in Section D or E that wetland indicators of one or 

 more parameters were lacking, probably due to normal seasonal or annual vari- 

 ations in environmental conditions. Specific procedures to be used will vary 

 according to the nature of the area, site conditions, and parameter(s) 

 affected by the variations in environmental conditions. A determination must 

 be based on the best evidence available to the field inspector, including: 



a. Available information (Section B) . 



b. Field data resulting from an onsite inspection. 



94 



