We have developed a simple flow shield that reduces the effects of flow noise on measurements of low-frequency underwater sound. The flow shield consists of a urethane dome that is cast in a vacuum to avoid formation of bubbles. The dome is filled with oil and secured over the transducer of a hydrophone using a hose clamp. The oil-filled flow shield was compared with two flow shield designs that have been used for marine acoustic monitoring, a thick, ballistic nylon covering and a thin, stocking nylon covering, and outperformed both.