Swim Lessons - Level 4 Stroke Improvement (class swims in deep end) Participants learn: Headfirst entry in a stride position in 9 feet of water, swim underwater for 3-5 body lengths, Tread water for 2 minutes, Survival float for 1-minute, Front crawl for 25 yards, Breaststroke for 15 yards, Butterfly for 15 yards, Elementary backstroke for 25 yards, Back crawl for 15 yards, Side stroke for 15 yards, Front and Backstroke open wall turns.