江

Three-drops water radical on the left - standard side-form of 水. 江 originally named the Yangtze specifically, largest waterway in the Chinese heartland, before generalizing to any major river. Sister 河 (originally the Yellow River) follows the same pattern: water radical plus phonetic giving a proper-river name that later widened.

Right 工 supplies the sound - gōng drifts to jiāng through an old g/j palatalization, the same shift seen across the 工-phonetic family (红 red, 虹 rainbow, 项 nape, 杠 pole). 工 itself depicts a carpenter's square; its meaning has no role in 江.