A reach is a segment of a stream, river, or arm of the sea, usually suggesting a straight, level, uninterrupted stretch. Wikipedia

An expanse, or widening, of a stream or river channel Wikipedia Disambiguation

A comparatively straight part of a river or channel between two bends Wikidata

A stretch of a watercourse which can be sailed in one reach (in the previous sense). An extended portion of water; a stretch; a straightish portion of a stream, river, or arm of the sea extending up into the land, as from one turn to another. By extension, the adjacent land. Wiktionary

Extended portion of land or water. Wiktionary (translation)