A pigeon-sized waterfowl sometimes dives into the water and often flies around the water, making a loud noise. What kind of bird is it?

Often work in pairs or in small groups. Good at swimming and diving, often swimming and diving in the open deep water near reeds and aquatic plants. As soon as people meet them, they immediately swim to reeds or grass, or dive into the water for a certain distance and then surface. They can dive into the water for a long time, sneaking up to 10 meters. They can only breathe with their nostrils out of the water, and their whole bodies are hidden underwater. When swimming, the body is above the water, the tail is often upright and swings frequently. Unless there is an emergency, generally do not take off, especially for long-distance flights. Flying speed is slow, flying speed is not high. It often flies close to the water surface and falls into the water surface or grass not far away.