Born and raised in the northern reaches of Manhattan, in Washington Heights, Harrison started swimming at eight-years-old. Every summer he and his siblings would return to his parents' home and swim in the lakes, rivers, and ocean around the Dominican Republic. Harrison swam for three years at George Washington High School while also playing baseball with the varsity team. For seven years Harrison was a New York City lifeguard, where he was called into action on numerous occasions to save adults and children alike. He joined the Imagine swimming family as a Pool Attendant and Lifeguard, and he soon joined Imagine's crew of teachers in the water.