MEMORANDUM ***

William F. Holdner appeals pro se from the district court’s judgment dismissing his 42 U.S.C. § 1983 action arising from the alleged improper regulation of Holdner’s former cattle ranch. We have jurisdiction under 28 U.S.C. § 1291. We affirm in part, vacate in part, and remand.

In his opening brief, Holdner failed to challenge the district court’s grounds for dismissal of his complaint, and therefore Holdner waived any such challenge. See Indep. Towers of Wash. v. Washington, 350 F.3d 925, 929 (9th Cir. 2003) (“[W]e will not consider any claims that were not actually argued in appellant’s opening brief.”). We affirm the district court’s dismissal of Holdner’s action but vacate the judgment in part and remand for the district court to dismiss Holdner’s action without prejudice.

The magistrate judge properly denied Holdner’s motion requesting review by a district court judge because the parties consented to a magistrate judge. See 28 U.S.C. § 636(c)(3) (when parties provide consent to magistrate jurisdiction, aggrieved party may appeal directly to court of appeals).

We reject as without merit Holdner’s contentions that his action qualifies as a *614 citizen suit under 33 U.S.C. § 1365(a), and' that the district court erred in denying discovery, the right to introduce additional evidence, and a requested hearing.

Appellees’ motion to take judicial notice (Docket Entry No. 11) is denied as unnecessary.

AFFIRMED in part, VACATED in part, and REMANDED.