Preface this with I was a good swimmer as kid. I learned to swim in diapers before I could walk.
However, all my swimming experience was in pools or lakes and when I was eight I visited the ocean for the first time.
We spent hours swimming and I was fine, increasingly becoming bold with how far I went out. Then learned what a rip tide is and made the mistake of fighting it. I swam against it for a good fifteen minutes until I became exhausted and began to drift out terrified. I was very lucky my sister realized and swam in and told my father. He dove in a got me let the current take us down the beach a bit and then swimming me back in to the shore. I felt very foolish, exhausted, and most of all fortunate that had my sister and father there with me. That five to ten minutes of fatigue making it a fight to stay afloat was most scared I remember being as a kid.