At the base of any aquatic food web lies a fundamental process: primary productivity. This is the conversion of inorganic matter, like carbon dioxide and mineral salts, into organic matter by photosynthetic plants such as algae. This process fuels the entire ecosystem, determining how much life a body of water can support.

The journey of increasing productivity in a body of water is known as eutrophication. This can be viewed as the natural “life cycle” or succession of a lake, a gradual aging process that transforms its character over time. This document will explain this life cycle by journeying through its distinct stages, using five real-world lakes as tangible examples of each phase.

1.1 The Idealized Succession

The idealized succession of a lake begins as oligotrophic (low productivity), becoming mesotrophic (medium productivity), eventually eutrophic (highly productive), and finally dystrophic—a bog stage in which the lake has almost been filled in by weeds and its productivity has greatly decreased. This progression is shaped by the lake’s original basin shape, climate, and surrounding soil, and it is not always a linear path; the process can be halted or even reversed.

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Our journey begins in the pristine, nutrient-poor waters of an oligotrophic lake, the youthful stage of its existence.