Merwarth placed 28th in women's 3-meter diving with a score of 341.50 at the Greensboro Aquatic Center. She will wrap up competition Friday on the 1-meter board.
Fowler swam the women's 500-yard freestyle in 5:04.87 for a 36th-place finish.
Fowler will swim the 200-yard freestyle on Thursday, while Beau Tipton makes his debut in the men's 100-yard butterfly and the 200-yard freestyle. Men's divers Daniel Valmassei and Anthony Liva are set for the 1-meter event Thursday. Preliminaries start at 10:00 a.m. EDT with the finals scheduled for 6:00 p.m.