A watercraft bilge pump is a mechanical device that is used to remove water that has accumulated in the bilge, or lowest part, of a boat or watercraft. The bilge pump is typically located in the hull of the watercraft and is connected to a hose or pipe that leads to the outside of the vessel. It consists of a motor, impeller, and housing, and is activated either manually or automatically by a float switch.

When the bilge pump is activated, the motor drives the impeller, which is a spinning blade that generates a flow of water. The water is then pumped out of the bilge and discharged through the hose or pipe. The bilge pump is an important safety feature of a watercraft, as it helps to prevent the vessel from sinking due to water accumulation in the bilge.

Watercraft bilge pumps are typically made from durable materials such as plastic or stainless steel, and are designed to withstand the harsh marine environment. They are an important part of a watercraft's safety and maintenance system, and should be regularly inspected and maintained to ensure they are functioning properly.