The question in Ballanger v. Johanns, 495 F.3d 866 (8th Cir. 2007), was technical and of no inherent interest (to me): whether the removal of woody vegetation from a wetland, without more, constitutes a "manipulat[ion]" of a wetland for purposes of 16 U.S.C. § 3801(a)(6)(A) or whether the U.S. Department of Agriculture had misconstrued the statute and was instead required to prove that any removal of vegetation actually impacted or reduced water flow. What is useful about the decision is the Eighth Circuit’s summary of the rules governing its review of administrative interpretations of statutes within their purview:

Whether we, as a matter of first impression, would have interpreted the statute in the same manner as the agency is of no consequence. We must defer to the agency's interpretation of the statute it is charged with enforcing unless that interpretation is contrary to the statute's unambiguous meaning. Fults v. Sanders, 442 F.3d 1088, 1090 (8th Cir. 2006). Similarly, we must defer to the agency's interpretation of its own regulation. See Thomas Jefferson Univ. v. Shalala, 512 U.S. 504, 512, 114 S. Ct. 2381, 129 L. Ed. 2d 405 (1994) ("Our task is not to decide which among several competing interpretations best serves the regulatory purpose. Rather, the agency's interpretation must be given 'controlling weight unless it is plainly erroneous or inconsistent with the regulation.'") (internal citation omitted). And, our overall review of the challenged agency action is deferential, such that we may only disturb agency actions that are, inter alia, "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." 5 U.S.C. § 706 (2)(A).

Agency interpretation sustained because ‛we cannot say the present regulation is contrary to unambiguous statutory language, that the agency's interpretation of its own regulation is plainly erroneous or inconsistent with the regulation, or that application of the regulation in this case was arbitrary or capricious.“