A chart plotter zoomed at the incorrect level will make all kinds of things disappear. Reefs even entire large islands are removed from the display some mistake for a "chart". That is just one of the reasons electronic chart plotters are so dangerous. Even more dangerous when used as the primary tool for coastal navigation. Depending on the time of day, cloud cover, and sun angle the reef may or not be visible. There simply is no substitute for proper use of the paper charts and visiable navigation aids once you are insight of land.