Anchor: Because it requires no ongoing effort or supervision to be effective, and it can be discontinued only after some (rather small) effort.
Entailed: It doesn't require an ongoing effort to be effective.
Contradiction: It requires an ongoing effort to be effective.
Contradiction: The pool is outside.
Contradiction: Many people were there.
Contradiction: People are swimming with disabled children.
Contradiction: Guys are working on a car.