Almost three-quarters of our planet is covered in water, but just three percent of all that water is freshwater! Unlike the saltwater in our seas and oceans, freshwater isn’t salty.

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Even though fresh water covers just a tiny bit of our planet, almost half of all the fish species on Earth live there. That’s because freshwater ecosystems are very diverse, from ponds to rivers to wetlands. Freshwater animals and plants have evolved to live in many different kinds of habitats.

Because we have so little fresh water, it is very important that we look after these habitats and keep them clean, healthy places for wildlife to live.


All plants need access to sunlight, since they make their food from the sun’s energy. To gather as much sunlight as they can, freshwater plants like water lilies have leaves that float on the surface of the water. But have you ever wondered why lily pads float, instead of just sinking to the bottom?

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Lily pads have hollow pockets of air hidden inside them. Just like a balloon floats in a bathtub, these air pockets work like a raft to keep the lily pad floating.


One of the toughest things about surviving can be finding food to eat. Some species have evolved ways to get food by harming other plants or animals – these plants or animals are called parasites.

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Worms called leeches survive by being parasites of freshwater fish. Leeches use their strong jaws to chomp onto the side of a fish, then they suck the fish’s blood. Blood is a good food source, since it’s full of minerals.

Predators get their food from other animals too, but there’s an important difference between parasites and predators. Predators kill their prey, but parasites like leeches want their hosts to stay alive so they can keep slurping up their blood. It may seem gross, but they’re just doing their best to survive!


Earth’s ecosystems are delicately balanced, since the plants and animals in them have lived together for so long. So when a new species arrive, it can cause big problems. A plant or animal that comes from elsewhere and harms its new ecosystem is called an invasive species .

Lake Mead has one of these invaders, and it’s called the quagga mussel. Quagga mussels are originally from Europe, but they made their way here to the United States in the water transported by large ships. Since then, they’ve leaped from lake to lake by clinging to boat bottoms and propellers.

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A tiny mussel may not seem very scary, but these mussels grow so quickly that they crowd out other plants and animals in the ecosystem. They eat up all the plankton in the water, leaving nothing for other freshwater species to eat. They also grow so fast that they clog up pipes, costing us lots of time and money in repairs.

The best way to stop these invaders is to keep quagga mussels from getting into our lakes and rivers in the first place! Boat owners should scrub their boats after taking them out of the water, in order to be sure that no mussels are clinging to them.

Explore Another Ecosystem