<p>Investigating the long-term evolutionary patterns of environmental vocabulary and their mechanisms of geographical spatial distribution can profoundly reveal how human environmental cognition is maintained or reshaped amidst natural and social changes. This also represents a significant challenge in current ecolinguistic research. As the world’s longest continuously used writing system, Chinese characters provide unique materials for examining the spatiotemporal evolution of environmental vocabulary. Water, as the core natural condition for human survival, production, and settlement formation, was among the earliest environmental objects to be continuously recognized and named, particularly within agrarian civilizations. Therefore, this study collected all water-body characters from China’s oldest dictionary and the modern dictionaries with the most extensive character collections, integrating them with toponymic data to systematically investigate the spatiotemporal evolution characteristics of Chinese water-body characters and their shaping factors. We propose the hypothesis: from historical times to the contemporary era, human cognition of the water environment has gradually enriched, accompanied by an increase in water-body characters; geographically, regions with abundant water environments also exhibit richer human cognition, reflected in higher diversity of water-body characters. The results indicate: (1) Water-body characters increased by 1226 over the span of 2000 years, reflecting the gradual development of more detailed cognitive classifications of water bodies as humans continuously engaged with, utilized, and managed water resources; over the past 40 years, water-body characters decreased by 432, possibly related to modern language standardization, the contraction of local vocabulary, and the weakening of traditional water environment experience. (2) Geographically, the distribution of water-body types in China generally exhibits a pattern of being more abundant in the southeast and sparser in the northwest (U = 8.5000, <i>p</i> = 0.0002). This pattern is constrained by regional hydrological natural conditions and is closely related to historical settlement development and human activities. The research demonstrates that the evolution of water-body characters is the result of the interplay among hydrological environment, cultural transmission, and social systems. Compared to the global trend of contraction in natural vocabulary across languages, the characteristic of long-term growth and continuity exhibited by the Chinese character system provides an important case for cross-cultural environmental cognition research. This study offers a replicable methodological framework for tracing environmental cognition through lexical systems and provides historically grounded insights for understanding long-term human-water relationships, and also a new linguistic perspective for language ecological protection and sustainable management in the context of climate change.</p>