Summer McIntosh came up short in a thrilling bid for her fourth-straight gold at the world aquatics championship in Singapore.

McIntosh took the bronze medal in the 800-metre freestyle at the world aquatics championship in a three-way duel to the finish.

The Toronto teenager, Olympic champion Katie Ledecky of the United States and Lani Pallister of Australia battled from start to finish, with Ledecky claiming her seventh world title in the distance.

McIntosh, seeking a fourth straight gold medal in Singapore, ran second to the American star before making her move on the final turn for a brief lead.

But Ledecky surged and delivered the knockout punch over the final 50 metres with Pallister closing fast behind her.

Ledecky finished in eight minutes, 5.62 seconds, with Pallister less than four-tenths of a second behind. McIntosh touched the wall 1.67 seconds after Ledecky.

Canada has now won seven medals at the world aquatics championships — six in swimming and one in diving.

McIntosh is also set to compete in the 400 individual medley on Sunday.