Complex sentence: Oronto Creek spilled over its banks, washing down trees and brush; its water flowed into the harbor, washing away boats, vehicles, asphalt, concrete, and trailers at the campground.
Split into simpler sentences: Oronto Creek spilled over its banks, washing down trees and brush. It spilled over its banks and the water flowed into the harbor, washing away boats, vehicles, asphalt, concrete, and trailers at the campground.