Great Britain's Rebecca Sherwin must qualify for the semi-finals of the 50m backstroke in Baku by way of a swim-off.
The Briton finished joint-16th in the heats with Netherlands swimmer Iris Tjonk, with the pair both clocking 30.22 seconds.
Only 16 swimmers can compete in the semi-finals, so the two will engage in a swim-off later today at the Baku Aquatics Centre.
Leading the way in qualifying was France's Pauline Mahieu (28.69s), closely followed by Carolina Pilhatsch (28.80s) of Austria.
Team GB's Sherwin finished seventh in the 200m backstroke final yesterday.
