1. The area in shallow fresh water and around lake shores where light penetration extends to the bottom sediments, giving a zone colonized by rooted plants.

2. In marine ecosystems the shore-area or intertidal zone where periodic exposure and submersion by tides is normal. Since the precise physical limits of tidal range vary constantly a biological definition of this zone, which essentially reflects typical physical conditions rather than rarely experienced events, is generally more useful. Thus in Britain the littoral zone is defined as the region between the upper limit of species of the seaweed Laminaria, and the upper limit of Littorina species (periwinkles), or of the lichen Verrucaria.