Mayagüez itself does not have a swimming beach — the harbour is industrial — but Playa El Seco, a few kilometres north of the city in the Algarrobo neighbourhood, is the closest decent stretch of sand and a favourite local spot for a quick dip after work. The beach is narrow and the water shallow; on weekends families set up shade tents and food stalls open along the road behind.
If you want better beaches, drive twenty more minutes north to Rincón or south to the wilder coastline at Cabo Rojo. But for a short, easy break from the city, El Seco does the job.