The Point-Rouge, Que., native clocked two minutes 10.37 seconds while Americans Caitlin Leverenz and Courtney Harnish placed second and third, respectively. On Thursday, Lacroix also won the 100-metre butterfly.
Lacroix wasn't the only Canadian to reach the top of the podium on Friday.
Dominique Bouchard of North Bay, Ont., took home gold in the women's 100-metre backstroke after tying for first with Denmark's Mie Nielsen in a time of 1:00.55.
Victoria's Hilary Caldwell was fifth and Danielle Hanus of Newmarket, Ont., sixth. It was Bouchard's third gold on the circuit this season after winning the 100 and 200-metre backstrokes last month.
Montreal's Victoria Poon added a silver in the women's 50-metre freestyle, clocking 25.82. Arianna Vanderpool-Wallace of the Bahamas won the race in 25.10. Caroline Lapierre-Lemire of Trois-Rivieres, Que., was fifth and Hannah Riordan of Cornwall, Ont., was seventh.
In the women's 400-metre freestyle, Victoria's Danica Ludlow earned a bronze in 4:13.78, with Samantha Cheverton of Pointe-Claire, Que., fourth. Elizabeth Beisel of the U.S. took the gold.
Team Ontario added a bronze in the men's 4 x 200-metre freestyle relay while Alec Page of Victoria was sixth in the men's 200-metre butterfly.