Wetlands are any land that is flooded with shallow water all or most of the time. They are a natural water holding system.
There are many types of wetlands. Among them, bogs, marshes and swamps are the three main types. The different types of wetlands have different kinds of plants. Only mosses（苔藓）and a few other kinds of plants can grow in bogs Grassy plants like cattails（香蒲）and reeds（芦苇） are the most common plants in a marsh. A swamp is a forest whose ground is underwater all or most of the time. Unlike bogs or marshes, a swamp is full of trees and bushes. It's not a good idea to go exploring a swamp without a guide. There are hidden pools of water, thick mud, and sometimes big crocodiles （鳄鱼）looking for their next meal.
Hungry crocodiles aren't the only animals that make the wetlands their home. Otters, turtles, frogs, snakes and many other animals do too. The water is home to many kinds of fish and crabs. Birds, including ducks, geese and cranes, use wetlands seasonally during their long migrations.
Wetlands are important because they provide habitats for plants and animals. A wetland system can also protect shorelines, make polluted waters clean, prevent floods, and restore underground water supplies.
According to WWF, more than half of the world's wetlands have disappeared since the beginning of the 20th century. If this continues, countless plant and animal species will surely die out. Without wetlands, cities have to spend more money to treat water. Don't feel helpless. Try to do your part to protect them right now. Here are some ideas.