Some crabs are causing many problems for rivers and streams. People are worried. They are trying to find ways to get rid of them.
These crabs are said to be a special food in China. Some people think that they were brought from China to California about ten years ago. Since then there are many more of these crabs.
These crabs are making the sides of rivers and streams weak. This can be very dangerous. If the sides of the rivers and streams get too weak they can break and cause flooding.
People are trying to find ways to keep the crabs out of certain areas. They are using screens to do this. The screens are big enough to let fish through but small enough to block the crabs.
Other people are collecting the crabs. They want to learn more about them. They hope to find a way to keep them from having babies.