What do you call a constructed waterway that is often grassed or vegetated?

A constructed waterway that is often grassed or vegetated is referred to as a swale. Swales are shallow, broad, and vegetated channels designed to manage water runoff, improve water quality, and promote groundwater recharge. They typically use vegetation to slow down water flow, allowing for infiltration and filtering of pollutants.

In landscape architecture and stormwater management practices, swales serve as effective tools for managing excess water from rainfall events, capturing it and allowing it to percolate into the ground. The grass and vegetation not only help stabilize the soil but also provide habitat for wildlife, improving the ecological value of the urban or residential areas where they're implemented.

In contrast, channels are usually engineered for efficient water flow without the vegetation component that characterizes swales. Streams and brooks refer to naturally occurring water bodies and do not typically denote constructed features. Thus, the term swale is specifically appropriate for a grassed or vegetated constructed waterway aimed at managing and directing stormwater effectively.