SA５　の執筆者は↓が分からないらしいのだ。嘘だろーーー

(boom)
３ a floating barrier used on a river, lake, or harbor to catch floating objects,
　to keep boats from entering, or to prevent an oil spill from spreading

・Large booms were brought in to help contain the oil spill.

http://learnersdictionary.com/definition/boom