We present a new flume for simulating the effects of both steady and oscillatory flow on the biogeochemical fluxes to coral reef communities based on a modified U-tube design. The flume is designed to recreate the in situ characteristics of a wide range of flows generated by wind, waves, and tides through two configurations. In the first configuration, a propeller driven by a 12-V DC motor generates steady, unidirectional flow speeds of 5 to 70 cm s(-1). In the second configuration, a piston driven by a 1500-W AC motor is used to generate oscillatory flows that are 5-12 s in period and have root-mean-square flow speeds of up to 50 cm s(-1), thus simulating the kinematics of real surface gravity waves in coral reef environments. Experimental coral reef communities are housed in a 3-m long test section covered with acrylic windows and lit with either 400- or 1000-W metal halide lamps generating photosynthetically active radiation ( PAR) irradiances of up to 1000 mu Ein m(-2) s(-1). The ratio of the volume of water in the flume to the projected area occupied by the experimental communities ranges from 1.1 to 1.7 m, making possible the expedient measurement of chemical fluxes to and from experimental reef communities. The total cost of the flume is just under $20,000 US for materials and approximately 700 person-hours of labor.