water's edge, shore, bank
湄 centers on the boundary where water meets land: a shore, bank, or water's edge.
湄 combines 氵 (water) with 眉, which likely contributes the sound and relates to the edge or brow of water.
Water 氵 meets the brow 眉 of the land, like the edge where a shore begins.
For ビ, imagine a bee buzzing along the water's edge: bee -> ビ, and the bee hovers right at the shore.