淤 appears in common compounds: 淤泥 (silt/mud), 淤血 (bruise/blood stasis), 淤积 (to accumulate sediment). The 氵 (water) radical hints at its connection to waterway blockage.
Three-drop water radical anchors the scene: silt and sediment collecting where water once moved. 淤 covers river siltation, blocked channels, and by extension stagnant blood - anything that 'gums up' a flow.
Right side supplies the sound: yū → yū (exact match). 於 is the classical-written form of the preposition 于 'at, in'; here it is purely phonetic and not contributing meaning. Same phonetic anchors 瘀 (blood stasis) - semantically a near-twin of 淤.
