A study by the Canadian authorities within the dashed outlined area indicates hazardous pinnacle-like features which may reduce the depths to as little as 30 percent of the charted depth. For example, where a depth of 29.26 meters/16 fathoms is charted, a depth of 8.68 meters/4.75 fathoms may exist nearby. An echo sounder may provide little if any warning when approaching these features.