The St. Sebastian's swim team joins forces each with Dana Hall to form one of the most competitive coed swim teams in the area. The combined team is led by Coach Matt Craven, of the elite Shawmut Aquatic Club, and St. Sebastian’s faculty member Carla Callini. Practices are held daily at Dana Hall throughout the winter and meets are held between December and February. Competition includes ISL rivals Milton Academy and St. George's School, in addition to other schools in the co-ed NEPSSA (New England Prep School Swimming Association). Over the past years, many St. Sebastian's swimmers have qualified and placed in the top 10 at the NEPSSA Championships.