Water Words Dictionary

Aquifer: An underground layer of sand, gravel, or permeable rock where water collects.

Bedrock: Solid rock that is underneath soil.

Biodiversity: A variety or richness of life on Earth. A key part of healthy ecosystems, biodiversity refers to the number of plants or animals within a single species, the variety of species themselves, and the variety of ecosystems. Diversity strengthens the potential of populations and species to respond or adapt to changing environmental conditions.

Bioengineering: This process uses living plants to restore stream banks, which in turn can control erosion, sedimentation, and flooding.

Brook: A natural, fresh-water stream that is smaller than a river.


Creek: A natural, fresh-water stream that is smaller than a river. This term is sometimes used specifically for small streams in coastal areas.

Deposition: A natural process in which sediment (sand, clay, gravel) falls out of the water, wind, or ice that carries it. In a stream, this process builds up stream banks – the opposite of erosion. Also called sedimentation.

Ecosystem: A system or area defined by a community of living organisms (plants, animals, bacteria) and their environment working together. A meadow, forest, and wetland are all different types of ecosystems.

Erosion: Wearing away of soil and rock from land by water, wind, ice, or gravity.

Floodplain: A low-lying land area along a stream or river that becomes covered with water when the stream or river spills over its banks. The flood water carries small rocks, gravel, and dirt – known as sediment – that builds up the land and enriches the soil over many years. Floodplains are important to people and wildlife. Flood waters spread out and slow down on a floodplain, protecting nearby communities from flood damage. Plants and trees in floodplains also filter pollutants and sediment.

Groundwater: Water that is stored in pores, cracks, and crevices below the water table and serves as the source of water for wells and springs.

Habitat: The area or environment where an animal finds the food, water, shelter, and space it needs to survive.

Hard Surfaces: When it rains, water runs off hard surfaces such as parking lots or sidewalks and enters storm drains. Many people think that water entering storm drains gets treated, but it does not; it gets dumped directly into streams. Hard surfaces speed the flow of water, causing erosion. In addition, water that runs over hard surfaces can become heated during warm weather and increase the temperature of stream waters, causing problems for fish and macroinvertebrates that need cool, well-oxygenated water.

Invasive Species: A species of plant or animal that is not native to a given ecosystem but whose presence might cause environmental harm to the system or harm to human health. Invasive species often thrive in new habitats because they have no natural predators in the new ecosystem to keep them in check.

Macroinvertebrates: A spineless animal visible without the use of a magnifying glass. Benthic macroinvertebrates, which live in the bottom of streams and wetlands, are good indicators of water quality because they live in the same area most of their lives and differ in their sensitivity to pollution. Which macroinvertebrates you find – or don’t find – in a stream indicates the pollution level of the water. Benthic macroinvertebrates include aquatic insects (such as dragonfly and damselfly larvae) and crustaceans (such as crayfish, snails, and clams). See our “Key to Stream Macroinvertebrates” for more macroinvertebrates and illustrations of each.

Meander: The “S” shape of many streams. Streams usually erode the outside of meander bends and deposit sediment on the inside of bends, causing the stream to move sideways across the land over time. Outside bends erode because the stream water moves fastest on the outside of the bend and moves more slowly on the inside.

Nonpoint-Source Pollution: Pollution that cannot be traced to a single source. Oil, gasoline, brake fluid, trash, fertilizers, pesticides, and animal waste that wash into waterways and damage water quality are considered nonpoint-source pollution. For more information, read “Sources of Pollution: Point and Nonpoint.”

Nutrients: Substances that promote growth. In a stream or other body of water, fertilizers, animal waste, and decaying leaves and grasses can be considered nutrients. In excess amounts, nutrients become pollutants.

pH: This measurement, which refers to the concentration of hydrogen ions in a solution, is used to measure whether a solution is acidic or alkaline (basic). The scale ranges from 1 (most acidic) to 14 (most alkaline), with 7 being neutral. At the acid end of the spectrum are solutions like lemon juice (2) and vinegar (3). Milk rates around a 6; pure water is a neutral 7. At the other end of the spectrum are ammonia (11) and bleach (12.5). The pH of the stream affects not only which aquatic organisms can survive there but other biological processes like reproductive cycles in fish.

Oxbow Lake: A water body that forms when a very windy meander bend gets cut off from a stream.

Point-Source Pollution: Pollution from a sewage treatment facility or industrial plant is called “point source” pollution because it comes from a single “point” – a pipe, ditch, or other discernable source carrying waste away from these facilities. For more information, read “Sources of Pollution: Point and Nonpoint.”

Pollutant: Any substance that causes harm to human health or the environment.

Riffle: Shallow, fast-moving water where the flow is broken by a bed of rocks.

Riparian Zone (also called a “Green Zone”): This term is used to describe the green ribbon of plants along the side of a stream, where the land and water can overlap. A riparian zone has distinctive plant species, soil types, topography, and wildlife because it is so close to the water. Riparian zones vary in size. For example, vegetation along a desert stream may be small and sparse while the vegetation along a mountain stream may be tall and lush. For more information, read "Riparian Zones."

River: A large, natural stream of water that runs into a larger body of water such as a lake or ocean.

Runoff: Rain or snowmelt that flows over ground surfaces. This water can collect nutrients, pollutants, and other materials from air or land and carry them into streams and lakes.

Sediment: Soil, rock fragments, and other material transported and deposited by water, wind, or other forces. For example, it is natural for stream waters to carry sediment. “Sedimentation” occurs when the rocks and dirt carried by the water build up on the bottom and sides of a stream.
Soil: Soil is a mixture of solids (minerals and organic matter), liquid, and gases that occurs on a land surface.

Stream: This term is used to describe any natural body of running water that moves over the Earth’s surface in a channel or bed. Rivers, creeks, and brooks are all considered “streams.”

Stream Banks: Areas on either side of a stream that restrict lateral water movement at normal water levels.

Turbidity: Cloudiness of water caused by suspended particles such as fine sediment and algae.

Watershed: The land area that drains into a stream or other body of water. Watersheds come in many different sizes; the watershed of a small creek may also be part of the watershed for a larger river. For example, water flows into the Mississippi River from more than one million square miles of land in 33 states and two Canadian provinces. Within that Mississippi River watershed are many smaller watersheds.

Water Table: The top of the underground area that is filled with groundwater.

Wetland: A wetland is an area of land where the soil holds water all or part of the year. A wetland usually holds a mix of plants – such as trees, shrubs, grasses – and shallow surface waters. They are found in low-lying areas on floodplains and coastal areas. Wetlands are very important natural systems. They provide essential habitat for a wide variety of plant life and many different kinds of amphibians, reptiles, birds, insects, mammals, and fish. Wetlands water filter runoff from the surrounding land, removing pollution and helping to keep water clean. Wetlands also provide natural and highly effective flood control. For more information, read "What Is a Wetland?"