In this subtitle the following words have the meanings indicated. “Duly designated agency” means any public body corporate, whether exercising local or regional authority, in any of the counties listed in § 8-1303 of this subtitle, which shall be officially designated by either or any of the counties which executes the programs and purposes of this subtitle within any of the counties. However, in Montgomery and Prince George’s counties, the Maryland-National Capital Park and Planning Commission is the duly designated agency of these counties to carry out the provisions of this subtitle. “Watershed” means the Patuxent River Watershed.