Entrainment is the process by which one thing is drawn along or transported by another thing. In the water world, it is commonly used to describe when fish or fish larvae are sucked into pumps or water diversions.

Water managers often use screens or other types of barriers to prevent fish and larvae from being drawn into pumps or diversions. Water managers also may reduce pumping of export water at certain times to minimize potential harm to fish, particularly declining species of fish such as Delta smelt and salmon.