<p>The National Marine Park of Alonnisos (NMPA), Northern Sporades, Greece, is among the largest marine protected areas (MPAs) in the Mediterranean Sea, covering an area of approximately 2,200 km². While it includes a small marine area designated as a no-fishing zone, bottom trawling is permitted in its waters from October to May at regulated distances from the shore. In this work, we use long term passive acoustic monitoring methods with a seafloor-moored hydrophone in the southern part of this MPA and quantify the underwater noise levels produced by this fishing activity during the winter months of 2022 to 2023. Throughout a 3-month recording period, bottom trawlers were detected almost daily, and their presence followed a regular temporal pattern that peaked at noon. Measured in 1/3-octave frequency bands, the root-mean-square received sound pressure levels showed that bottom trawling noise was a dominant feature of the underwater soundscape. The results are discussed with respect to the noise monitoring requirements of the European Union’s Marine Strategy Framework Directive and the need to mitigate underwater noise pollution in marine protected areas.</p>