• Sabelotodo

    Senior Member
    English, United States
    I am not certain, but here is a dictionary definition of to entrain: to pull or draw along after itself; [Chemistry] to carry (suspended particles, for example) along in a current.

    I think that it means the oil that is carried along by the flowing water. Wait for more suggestions to be sure.


    Chambers English Dictionary gives this as the second meaning of entrain
    verb transitive to transport one substance, e.g. small liquid particles, in another, e.g. a vapour (physics); to suspend bubbles or particles in a moving liquid (physics); to draw after (archaic).