Manitou Passage Underwater Preserve is a protected area in Lake Michigan around North Manitou Island, South Manitou Island, and much of the shoreline bordering Sleeping Bear Dunes National Lakeshore. Because this passage has long carried substantial commercial traffic traveling both upbound and downbound on the lake, it became especially rich in freighter wrecks. The preserve contains thirty-three recreational diving sites, most within the national lakeshore boundary, featuring shipwrecks and other maritime remains such as old docks. Better-known sites include the Alva Bradley, PJ Ralph, JB Newland, Congress, Three Brothers, and Jarvis Lord.