The main river markets include the Rhine/Danube system in Europe, the Mississippi and its tributaries in North America, and the Yangtze and Yellow Rivers in China. Due to navigation limitations such as shallow draft and bridge clearance, river cruise ships are smaller, commonly with 200 guests or less. Due to the scale issue, they have fewer onboard entertainment and amenities. Still, unlike sea cruises, they have the opportunity to resupply along the route with local catering, products, and entertainers.