According to Heriot-Watt University: "Salvage operations in the 20’s, 30’s and as recently as the 1970’s have left only seven major wrecks in the area. ... In addition to these sites, there are several areas of debris and depressions on the seabed created during salvage operations ...."  (ScapaMAP: the Scapa Flow Maritime Archaeology Project)  So while many of the wrecks have been recovered, there's still a possibility that valuable materials remain.