All manner of concrete, steel, and stone rubble from dredging, demolition projects, and other construction is used as artificial reef materials. This material is generally available at very low cost or free from construction companies who are more than happy to get rid of it. Transportation costs determine where this material is used by the Reef Program.
Looking roughly southeast, with the diving cove in the foreground. The natural basin of the valley is evident, as well as one of the two dams, at right. The water level looks pretty high, with a little snow on the ground.