The KQ507 crash in Cameroun pretty much buried itself in mud and there was very little debris at ground level making discovery and recovery very difficult.
In mud, yes.
In very shallow water over mud, yes OK.
With 50 m or more of water over mud. Nope. The plane ail fragment if it hits the water at high speed. Some of these pieces will be small with little momentum. Some won't be very aerodynamic (? hydrodynamic). Can you see a detached aileron flying through this much water and digging itself into the mud.
Even a high velocity (supersonic) bullet will travel a short distance, rapidly decelerate due to deformity and tumbling, and then slowly sick to the bottom. A bullet has much greater density, (and therefore greater momentum relative to surface area) than a plane. But if you fired a bullet into mud, sure it will go below the surface.