Trophic State: A Useful Scale for Classifying Lakes Based on Biological Productivity: FA268, 6/2025

Abstract

Lakes are diverse and come in all shapes and sizes. The Trophic State Classification System allows people to group waterbodies into one of four categories, called “trophic states,” based on their level of biological productivity. Knowing what these terms mean can help you understand how your waterbody compares to others, and what changes in its water quality over time could mean. This publication explains how water chemistry is used to determine a waterbody’s trophic state; what criteria are used to define the four trophic states; which trophic state category your waterbody fits into; and how the Trophic State Classification System can be useful.