Occurring in coastal areas or inland, water in wetlands can be fresh, brackish (somewhat salty), or salty. Examples include mountain meadows, marshes, vernal pools, and swamps, among others. Wetlands are highly productive and support a wide range of aquatic organisms including mammals, fish, birds, invertebrates, and plants. Wetlands benefit people by cleaning water, protecting communities from flooding, removing carbon from the atmosphere, and stabilizing shorelines.

Wetlands receiving water from groundwater tend to stay wet longer than those fed only by surface water, providing more stable conditions for natural communities. However, when groundwater levels are lowered, the connection to the wetland is lost, water becomes unavailable, and valuable natural habitats shrink.

Consequences of Intensive Pumping

• Plants and animals that depend on wetlands lose the habitat they need to survive and can die.
• Migratory birds and other animals lose a necessary water, shelter, and feeding source, disrupting large-scale animal movement, such as the Pacific Flyway, one of the most important global migration pathways for birds.
• Water quality deteriorates.
• Hunting, fishing, birding, boating, and other recreational opportunities are lost.
• Availability of water for human use decreases, negatively affecting domestic, industrial, and agricultural use.

Lying at the interface of land, freshwater, and oceans, estuaries host a dynamic range of biological and physical processes. Estuaries are crucial in the exchange of energy and materials between these realms, creating a diversity of habitats that support a variety of species.⁸ Estuaries are some of the most productive areas on Earth, producing or collecting high amounts of organic material that provide an important food source for resident and migratory animals. Many animals also rely on estuaries for a place to breed or rear offspring, and for migration stopovers.

California has over 500 estuaries in a great diversity of sizes and types, ranging from the Sacramento-San Francisco Delta Estuary—the largest estuary on the west coast of the Americas—down to tiny, intermittent streams reaching the ocean. For many of these abundant smaller estuaries, groundwater can be an important source of freshwater, particularly in our intermittent river systems or where upstream surface water use is high. Estuaries occur in some of California's biggest cities: San Francisco, San Diego, and Los Angeles. These coastal estuaries play an important role in creating a natural buffer zone against coastal storms and sea level rise for our cities and communities. In addition, they are popular recreational destinations for fishing, birding, boating, and hiking.

Most rivers begin their journey high up in the mountains or hills, where winter snow melts and rain falls. Yet snowmelt and rainfall can also seep into the ground to form groundwater. Groundwater connects to rivers and streams on a permanent or intermittent basis. When groundwater levels are higher than the flowing river, groundwater adds to the river increasing its flow. In arid climates found in some parts of California, groundwater commonly contributes all or some of the water flowing down a river, particularly during the dry summer and fall months.

When there are dry conditions, insufficient rainfall or excessive groundwater pumping, groundwater levels can drop below the elevation of the riverbed. Depending on the aquifer conditions, groundwater pumping occurring farther away can still impact groundwater levels below the riverbed. In some cases, impacts from groundwater pumping can also be delayed, meaning that groundwater levels can continue to drop after pumping has stopped. These impacts can cause river flows to be depleted as surface flows sink and less surface water is available to replenish groundwater. In some cases, rivers and streams can go dry in certain segments and/or for longer periods of time as compared to their natural state. This is problematic because groundwater is often a source of much needed cold water for rivers and streams during the hot summer and fall months. Areas where groundwater flows into streams and rivers provide habitat and refuge to many native fish that need cold water to survive, such as salmon and steelhead trout.

Consequences of Intensive Pumping

• Because rivers and streams frequently carry our water supplies, depleted rivers result in less water available to support communities, agriculture, and our economy.
• Groundwater depletion can cause reaches of rivers and streams to have a greatly reduced flow, or even to go dry at certain times of year. This can fragment wildlife corridors, impair migration of fish, such as salmon and steelhead trout, and reduce or eliminate riverine habitats.
• Groundwater often provides summer and fall base flows in streams and rivers. Depletion of groundwater can drastically lower base flows and decrease habitat availability during the months of the year when species are at greatest risk of stress from high water temperatures.
• Decreased groundwater levels in riparian areas and on floodplains mean that trees and other plants must have deeper root systems to reach sufficient water for survival and growth. Some trees and other plant species cannot adjust quickly enough to survive. Other species no longer have the conditions necessary for recruitment, decreasing the regeneration of floodplain and riparian forests.
• Lower groundwater levels can eliminate the input of cold water or reduce the total amount of water flowing in a river or stream. Decreased groundwater input can cause the remaining stream water to warm as it gets shallow. Warmer water can affect wildlife behavior, and harm important spawning habitats for salmon and other fish.

Springs and seeps supply surface flows of water from groundwater aquifers. While these flows are often limited, they may support critical GDEs, including endangered, rare and/or endemic species of mammals, plants, mollusks, fish, and insects that have no other source of water and sometimes no other alternative habitat. Some of the most important springs are found in deserts, and serve as the only watering hole for hundreds or thousands of acres. These springs constitute important watering holes and stopover points for wildlife on the move, including large mammals such as the desert bighorn sheep.

Many springs and seeps are particularly sensitive to even slight declines in groundwater levels and can permanently disappear when groundwater pumping decreases regional groundwater levels. Springs with substantial flow can serve as the headwaters for our streams and rivers, directly sending groundwater downstream. Smaller springs and seeps, especially in arid areas, may support a vibrant but limited riparian corridor before disappearing. In California desert areas, springs and seeps as well as their riparian areas provide islands of habitat for migratory birds. Groundwater from springs and seeps can be colder than surface water, providing important or unique habitat conditions such as the spawning habitat for salmon found in the Shasta Valley. In other places, springs and seeps can be warm or hot because the groundwater is heated under the Earth’s surface, such as in the volcanic area at Lassen National Park or along the Amargosa River in the Mojave Desert, where groundwater from older and deeper reserves provide uniquely important habitat conditions.

Consequences of Intensive Pumping

• Lower groundwater levels can reduce or eliminate springs and seeps. Resident fish, plants, and invertebrates can lose their habitat and die.
• In some cases where unique plants or animals rely on a seep or spring, the loss of this habitat can cause an entire species to go extinct.
• Migratory birds and animals lose a necessary water source.

Vegetation dependent on groundwater access it through their roots. If those levels change rapidly, plants lose access to groundwater and can die. Gradual decreases in groundwater levels sometimes allow plants grow deeper roots to access lower groundwater or to adapt to less water. However, groundwater declines often favor opportunistic invasive plants that displace and degrade natural habitats.

There are two types of groundwater dependent plants—shallow rooted and deep-rooted plants. Shallow-rooted plants rely on groundwater being close to the Earth’s surface and can often be found in groundwater discharge areas such as mountain meadows or coastal wetlands. These shallow-rooted plants are adapted to having their roots submerged in groundwater. Deep-rooted plants (“Phreatophytes”) are not submerged in groundwater and access groundwater in shallow aquifers.

Shallow-rooted and deep-rooted plants respond very differently to declines in groundwater levels. Shallow-rooted plants die immediately when groundwater recedes and soils become dry. However, deep-rooted plants such as mesquite trees are somewhat more resilient to groundwater decline since they are able to extend their rooting systems. Yet they will die out eventually if the depth to groundwater is too far or the rate of groundwater decline is too fast.

Consequences of Intensive Pumping

• Vegetation becomes stressed and may die.
• Local animals lose their habitat and must relocate or die.
• Reduced seedling survival, impaired recruitment, and a reduction in total vegetation.
• Recreation opportunities are lost.
• Invasive plants can take over, eliminating native habitat, and create a nuisance or increased fire risk.