An aeration system has aerators that remain generally full of air when the supply of pressurized air is turned off or vented. Water does not reach the bubble discharging holes of the aerator, which are kept from plugging. The aerator has a body with a hole through a wall of the body to discharge bubbles. The hole is surrounded by a skirt at the wall of the body. The skirt extends to below the elevation of the hole. The aerator body is connected to a source of pressurized gas through an open bottomed chamber. An opening between the aerator body and the inside of the chamber is located below the elevation of the hole. When the supply of gas is off, water enters the chamber and possibly the skirt. However, the water can only rise until it has reached the skirt and the opening, both of which are below the hole, and the entire aerator body is kept dry. Aerator fouling is reduced, and the aerator begins to produce an even flow of bubbles quickly when the supply of gas returns.