competitive swimmers have that much more endurance in the water than the average swimmer.
I swam from a young age and did swim team during elementary school, and I was always a strong swimmer but didn’t keep up with training after I quit. One year during uni wrestling cross training we were doing laps in the pool and the women’s polo team was also there at the same time, so our coach told us to go play with them for a bit. Despite both wrestling and polo demanding high endurance and total body fitness the muscles used are completely different and we had a fun session of almost drowning while the ladies shoved us underwater and hucked balls over our submerged heads.