A river delta is a special place where a river meets the sea. It looks like a big triangle that is made of mud and sand.
Imagine that you have a bathtub full of water and you put some sand in it. If you let the water drain out of the bathtub, you will see that the sand collects in one place. That's kind of how a river delta is formed.
When the river meets the sea, it slows down and drops all the mud and sand it has been carrying along with it. Over time, this mud and sand builds up and creates land. And that's how you get a river delta!
There are lots of different plants and animals that live in river deltas because it's a really unique environment. The land is always changing because the river and sea are always moving and shaping the land.
So if you ever go to a river delta, remember that you're seeing a really special place where the river and sea come together to make something new!