Surface water systems can be classified as lentic (like a lake) or lotic (like a river) based on how water flows through them. A new method called the Freshwater Continuum Classification (FCC) uses residence time to objectively determine if a system is lentic, lotic, or oscillating between the two. By analyzing how long water stays in a system, the FCC can classify water bodies accurately. In a study of 15 river segments in Texas, the FCC successfully identified lentic, lotic, and oscillating systems, providing a reliable way to classify surface water systems regardless of their size or type.