Two readings, two different words. bó is the verb: a boat 泊 at a harbour, a car 泊 at the kerb. The noun meaning lake is pō, the reading inside 湖泊.
usage
In Hong Kong and Cantonese-speaking areas 泊车 is the ordinary word for parking; mainland standard usage prefers 停车. The same bó sits in 淡泊, living plainly and without ambition, where the picture is a boat lying still.
Three water drops on the left - the side-form of 水 - mark 泊 as something to do with water. It anchors the boat-mooring sense and groups 泊 with 海, 河, 湖, the wider water-body and water-action family.
Lends its sound, drifting from bái to bó. It heads a small phonetic series including 伯, 拍 and 柏 that all share the 白 sound stem. The white meaning is unrelated to mooring boats.
