Spoil Area, Chart
Spoil Area refers to an area which has been used or is currently being used (unlikely) as a dumping area for debris. For example, the material from a dredging operation or construction site. It does not necessaraily denote a bad thing but it is there to inform you that the bottom might contain material or debris that you might not want to anchor in or swim in. In some instances, depending on the material dumped at the site, you stand the chance of fouling your anchor.