Which type of water ecosystem is characterized by flowing water?

The type of water ecosystem characterized by flowing water is the lotic ecosystem. Lotic ecosystems encompass rivers, streams, and other environments where water moves continuously in one direction. This movement plays a significant role in shaping the habitat, influencing factors like oxygen levels, sediment transport, and the types of organisms that can thrive there.

In contrast, lentic ecosystems describe standing water environments such as ponds and lakes, where water is relatively still. Marine ecosystems pertain to saltwater environments like oceans and seas, which differ from freshwater lotic ecosystems. The term "vertebrate ecosystem" is not a standard classification of aquatic ecosystems, as it refers more broadly to ecosystems inhabited by vertebrates regardless of whether the water is flowing or standing. Thus, the defining characteristic of flowing water clearly identifies the lotic ecosystem as the correct answer.