An opto-acoustic flowmeter can include an optical waveguide and an emitter that emits acoustic energy in response to flow, the acoustic energy comprising a flow rate dependent parameter. A flow rate measuring method can include configuring an emitter so that flow into or out of a tubular string causes the emitter to emit acoustic energy, arranging an optical line so that the acoustic energy is received by an optical waveguide of the optical line, and detecting optical scatter in the optical waveguide. A well system can include multiple locations where fluid is flowed between an earth formation and a tubular string in a wellbore, multiple emitters that produce an acoustic vibration corresponding to a flow rate of the fluid, an optical line that receives the vibrations, and an optical interrogator that detects optical scatter in an optical waveguide of the line, the scatter being indicative of the vibrations.