noun
sea wall; breakwater
A structure built to protect a harbor or coast from waves.
港の外側に波除けが築かれた。
A breakwater was built outside the harbor.
防波堤 is a more technical term for breakwater, while 波除け is a common, descriptive word.
Compound of 波 (nami, 'wave') and 除け (yoke, 'protection, warding off').