From Bai Juyi's (
白居易, Tang) 《
春题湖上》 or similarly attributed Tang lake-poetry (the line is anthologized across 《
白氏长庆集》 and later collections).
花 here means 'like flowers' — the wave crests scatter into petal-shapes. Paired frequently with
雁点青天字一行 in shi couplets about water and sky.