40 Fun Facts About Freshwater Biome

Which famous Scottish body of water holds more fresh water than every lake in England and Wales put together?

Loch Ness is only Scotland's second-largest loch by surface area, but its great depth makes it the biggest body of fresh water by volume in the British Isles.

Fresh water makes up under 3% of Earth's water, and most of that small share is stored where?

Glaciers and ice caps lock up roughly two-thirds of the planet's fresh water, and most of the rest lies underground. Liquid water at the surface is only a tiny sliver of the total.

For straining sediment and pollutants out of passing water, wetlands are often nicknamed nature's what?

Kidneys is the nickname because wetland plants and soils trap sediment and soak up excess nutrients before the water moves on. Some towns even build artificial wetlands to treat their sewage.

Which ocean predator swims so far up rivers that it has turned up in the Mississippi as far inland as Illinois?

Bull shark bodies can adjust to both salt and fresh water, a trick most of their relatives lack. The species is so at home in one Central American lake that it is also called the Lake Nicaragua shark.

South America's boto, the largest of the river dolphins, is famous for slowly turning which colour as it matures?

Pink skin appears in adults as repeated scrapes wear away the grey surface, and males, which fight more, end up the brightest. Calves are born dark grey.

Which African river giant oozes a red fluid nicknamed 'blood sweat' that works as its own sunscreen?

Hippopotamus skin releases the fluid colourless, and it turns red-orange within minutes. It is neither blood nor sweat, and its pigments also slow the growth of bacteria.

Which lake, the deepest on Earth, holds more water than all five North American Great Lakes combined?

Lake Baikal in Siberia holds 22 to 23% of the world's fresh surface water. It is also the oldest lake on Earth, at 25 to 30 million years.

The longest beaver dam known, big enough to be spotted on satellite images, lies in a national park in which country?

Canada's Wood Buffalo National Park, in Alberta, holds the record dam. Beaver ponds create wetlands that many other species depend on, which is why ecologists call the animal a keystone species.

Which Australian stream hunter shuts its eyes, ears and nostrils underwater and finds prey by sensing electric fields?

Platypus bills are packed with sensors that pick up the faint electricity made by the muscles of shrimp and insect larvae. The male is also one of the few venomous mammals, with a spur on each hind foot.

Which South American swamp dweller, the largest living rodent, can hold its breath underwater for up to five minutes?

Capybara eyes, ears and nostrils sit near the top of the head, so the animal can keep watch while almost fully submerged. It lives in every South American country except Chile.

Which frilly-gilled salamander, native only to lakes in the Valley of Mexico, keeps its larval form for life?

Axolotl adults keep their feathery gills, never leave the water and can regrow lost limbs. Invasive carp and tilapia have pushed the wild population close to extinction.

Which South American river fish owes its man-eating reputation largely to a travel book by Theodore Roosevelt?

Piranha schools stripped a cow to the bone in front of Roosevelt, but local fishermen had staged the show by penning the fish and starving them for days.

Despite its name, South America's electric eel is not a true eel but belongs to which group of fishes?

Knifefishes mostly make only weak electric fields for finding their way in murky water. The electric eel is the exception, able to stun prey with shocks of up to 860 volts.

The giant water lily of South America, with leaves up to three metres wide, was named in honour of which monarch?

Queen Victoria had only just come to the throne when botanist John Lindley named the plant for her. With the load spread evenly, a single floating leaf has held 110 kg.

Which Nile wetland plant, best known as an ancient writing material, has stems buoyant enough to build boats?

Papyrus is a sedge that grows in dense stands in shallow water, and parts of the plant can even be eaten. The Egyptians pressed strips of its stem into one of the first kinds of paper.

In which acidic type of wetland have ancient bodies such as Denmark's Tollund Man been found with skin and hair intact?

Bog water is highly acidic, cold and short of oxygen, which tans skin like leather while dissolving bone. Tollund Man was so well preserved that he was mistaken for a recent murder victim.

Which of North America's Great Lakes is the largest freshwater lake in the world by surface area?

Lake Superior holds enough water to cover all of North and South America to a depth of 30 centimetres. French explorers named it simply the upper lake, because it sits above Lake Huron.

Which South American lake, home to floating reed islands, is often called the highest navigable lake in the world?

Lake Titicaca sits 3,812 metres up in the Andes, and the Uros people make its famous islands by hand from layers of cut totora sedge.

Which river carries more water to the sea than the next seven largest independent rivers combined?

The Amazon supplies about 20% of all the river water that flows into the world's oceans. Whether it or the Nile is the longest river on Earth is still disputed.

Which American wetland did writer Marjory Stoneman Douglas famously describe in print as a 'River of Grass'?

The Everglades are really a slow-moving river some 60 miles wide, sliding south over limestone to Florida Bay. Douglas's book came out a month before the national park was dedicated.

Which fish hatches in freshwater streams, grows up at sea, then finds its home river again largely by smell?

Salmon learn the scent of their birth stream as juveniles and follow it back years later to spawn. Fish that live at sea but breed in fresh water are called anadromous.

European eels leave their rivers and swim thousands of kilometres across the Atlantic to spawn in which sea?

The Sargasso Sea is a journey of about 6,500 km from Europe, and nobody has yet seen the eels mating there in the wild. Their life story puzzled naturalists for thousands of years.

Which insect spends most of its life as an underwater nymph, then emerges as a winged adult with no working mouth?

Mayfly adults cannot feed and live only to mate, and the females of one American species last less than five minutes. Their nymphs are so sensitive to pollution that they are used to check the health of streams.

Which fast-flying pond insect can spend up to five years underwater as a nymph before it grows wings?

Dragonfly nymphs are fierce hunters that shoot out a hinged lower lip to grab tadpoles and even small fish. Most adults then live for five weeks or less.

Which long-legged insect glides across pond surfaces on legs coated in thousands of tiny hairs that repel moisture?

The water strider's whole body is covered in these hairs, more than a thousand to the millimetre, so splashes and raindrops simply roll off. It is also known as the pond skater.

The Okavango River never reaches the sea, instead spreading into a vast inland delta in which African desert?

The Kalahari swallows nearly all of it: about 96 to 98% of the water entering the delta is lost to evaporation, thirsty plants and seepage into the ground.

The Ramsar Convention, the global treaty protecting wetlands, takes its name from a resort city in which country?

Iran hosted the 1971 conference at Ramsar, on the Caspian Sea coast, where the treaty was adopted on 2 February. That date is now marked every year as World Wetlands Day.

In Australia, a U-shaped lake left behind when a river cuts off one of its own bends is called a what?

Billabong is the Australian name for what is elsewhere called an oxbow lake. One forms when a river erodes through the narrow neck of a loop, often during a flood.

What name is given to a stream that flows into a larger river instead of running directly to the sea?

Tributary streams add their water to a main river, while a distributary does the opposite and branches away from it, as the channels of a river delta do.

What is the name for the process in which fertiliser runoff feeds algal blooms that strip a lake of oxygen?

Eutrophication can happen naturally, but sewage and farm runoff speed it up enormously. When the algae die, the bacteria that break them down use up the oxygen that fish need.

Which branch of science, named from the Greek word for lake, studies rivers, ponds, wetlands and other inland waters?

Limnology was named and founded by the Swiss scientist François-Alphonse Forel, who built the field on his studies of Lake Geneva. He first described it as the oceanography of lakes.

What do ecologists call the shallow edge of a lake, where sunlight reaches the bottom and rooted plants can grow?

The littoral zone takes its name from the Latin word for shore. Farther out lies open water, and beneath that the depths where too little light arrives for plants to grow.

In summer, which thin middle layer of a deep lake separates warm surface water from the cold water below?

The thermocline is where the temperature drops fastest with depth, and its position can shift through the day. In temperate lakes the layers break down with the seasons and the whole lake overturns.

Which African Great Lake holds more fish species than any other lake on Earth, including at least 700 cichlids?

Lake Malawi's cichlids evolved within the lake itself, and some species are confined to rocky stretches of shore only a few hundred metres long.

The word 'meander' comes from an ancient river, famous for its winding course, that flows through which modern country?

Turkey still has the river, now called the Büyük Menderes, which winds west to the Aegean. The ancient Greeks knew it as the Maiandros and gave it a river god of the same name.

Which tiny floating pond plants, sometimes confused with algae, include the smallest flowering plants on Earth?

Duckweeds of the genus Wolffia have no roots and look like specks of cornmeal on the surface. Their flowers are the smallest known, only 0.3 mm long.

Which European arachnid spends almost its whole life underwater, breathing from an air supply held in a silk chamber?

The diving bell spider rests, hunts, mates and lays its eggs below the surface, coming up only briefly to restock its air. No other spider is known to live this way.

Which South American floodplain, lying mostly in Brazil, is the largest tropical wetland in the world?

The Pantanal has roughly 80% of its floodplains under water in the rainy season, and it shelters one of the largest and healthiest jaguar populations on Earth.

Which waterlogged landscapes cover only about 3% of Earth's surface yet hold more carbon than all the world's forests?

Peatlands are the largest natural carbon store on land, because soggy, airless ground stops dead plants from fully rotting. Drainage, farming and fires are their main threats.

Which African river is the deepest in the world and the only major river to cross the equator twice?

The Congo has measured depths of around 220 metres. Because its basin lies on both sides of the equator, some part of it is always in a rainy season, which keeps the flow steady.