Navigable servitude is a legal concept that says that even if you own a piece of land on a river or a stream, the government has the right to use it for navigation. That means that boats and ships can travel through your land, even if you don't like it.
It's kind of like having a big slide in your backyard that you let your friends use. Even though you own the slide, you're letting other people use it for a specific purpose. In the same way, even though you own the land next to a river, the government is allowed to use it for boats to pass through.
But don't worry, just because the government has the right to use your land for navigation doesn't mean they can just do anything they want. They still have to make sure they're not causing any harm to your property. And if they do damage your property, they have to compensate you for it.
So, even though it might seem strange that other people can use your land, it's just a rule that helps everyone get around and use the river.