A river lock is a waterway structure that helps boats and ships navigate changes in water levels along rivers and canals. It consists of a chamber where vessels can enter and be raised or lowered to match the water level of the section ahead. This process allows boats to travel smoothly over obstacles like dams or waterfalls. Locks operate by filling or emptying the chamber with water through gates. When a vessel enters, the gates close, and water is either added or drained to adjust the height. This system is essential for maintaining navigation routes and facilitating trade and transportation on waterways.