Dongzhai Harbor National Nature Reserve protects one of Hainan's most important mangrove wetlands, east of Haikou. The reserve is about tidal channels, birdlife, mudflats, and the strange root systems that make mangroves feel half-land, half-sea.
It is a good counterweight to Haikou's streets, museums, and shopping districts. Time the visit with tides if possible, and bring patience: wetlands are most rewarding when you slow down enough to watch birds, water, and fishing life rather than expecting a dramatic single viewpoint.