name of river in China
瀘 is a rare kanji used primarily as the name of a river in China. Its standalone meaning is tied to that specific place name and has no broader conceptual center.
瀘 combines 氵 (water) with 盧, which likely contributes the sound. The character was created to write the name of the Lu River in China.
The water radical 氵 beside 盧 points to a river. Think of the Lu River flowing beside the ancient city of Lu.
For ロ, imagine a low, slow-moving river: low -> ロ, and the water 氵 flows gently through the Lu region.