The mowing apparatus is made up of a long, narrow cutting assembly, a boat and two booms, one on each side of the boat, attaching the cutting assembly to the boat. There is a flotation tank at each end of the cutting assembly and the forward end of each tank is pivotally attached to the aft end of a boom. The forward ends of the booms are pivotally attached to the boat at about gunwale height and well toward the bow. All the pivotal connection axes are horizontal and perpendicular to the vertical plane through the centerline of the boat, allowing the cutting assembly to be raised and lowered between the surface of the water and the bottom of the body of water. The raising and lowering are done by allowing water into the tanks to cause the cutting assembly to sink and forcing the water out of the tanks with air to raise the cutting assembly. The cutting assembly is a sawtoothed blade operating between two sawtoothed plates. The end wise oscillations of the blade are powered by a pneumatic actuator. The tanks are sized and positioned to hold the cutting assembly a specific distance from the bottom when the tanks are flooded and to float the cutting assembly clear of the water when they are full of air. The bottoms of the tanks are shaped so that they plane on the water surface at relatively high boat speeds.