A body found in the Yarra River had been there about two days, police say.

A passer-by spotted the body of a man, believed to be in his late 30s, about 10am on Tuesday near Banana Alley, which runs between Flinders Street train station and the Melbourne aquarium.

The man is yet to be identified and it is not yet known if the circumstances are suspicious.

Water police retrieved the corpse from the water.

Police are appealing for witnesses.