Fresh waters

Although fresh water lakes, ponds, rivers, and streams make up a very small portion of Earth’s surface, they are critical for our water supply for homes, industry, and agriculture and play important ecological roles. They are major recreational resources but are easily polluted. Dominant plants are floating algae, referred to as phytoplankton. Along shores and in shallow areas are rooted flowering plants, such as water lilies. Animal life is often abundant. Open waters have many small invertebrate animals (zooplankton)—both herbivores and carnivores. Many species of finfish and shellfish are found.

Rivers and streams are important in the biosphere as major transporters of materials from land to ocean. Fresh waters are economically important to people for their drinking water, production of energy, fish, bird life, and for recreation and transportation.

Estuaries—areas at mouths of rivers where river water mixes with ocean waters—are rich in nutrients and usually support an abundance of fish. They are important as breeding sites for many commercially significant fish.

Human activities have several adverse impacts on rivers and streams, including water pollution and the effects of dams, which are built to contain or divert the water of rivers or streams. Pollution alters the physical environment and changes the biotic component downstream from the pollution source. A dam causes water to back up, flooding large areas of land and forming a reservoir, which destroys terrestrial habitat. Below the dam, the once powerful river is often reduced to a relative trickle, altering aquatic ecosystems.

Open Ocean

The open ocean biome includes open waters of much of the oceans. These vast areas tend to be low in nitrogen and phosphorus—chemical deserts with low productivity and low diversity of algae. Many species of large animals occur but with low density.