A beaker of water sits on a scale. If you dip your little finger into the water, what happens to the scale reading? Assume that no water spills from the beaker in this process.
The scale reading goes up. When your finger is in the water the water applies an upward buoyant force on your finger. By Newton's third law, your finger applies an equal and opposite force down on the water. The scale reading equals the normal force between the scale and the beaker - the normal force equals the force of gravity on the beaker and water plus the extra force associated with your finger.
Another way to look at this is that putting your finger in the water raises the water level in the beaker. This raises the pressure at the bottom of the beaker, as well as the downward force exerted on the bottom of the beaker by the water. The upward force from the scale must increase by the same amount to compensate.