Tailwater refers to waters located immediately downstream from a hydraulic structure, such as a dam (excluding minimum release such as for fish water), bridge or culvert.

Tailwater can refer to a type of fishery

Fishery

Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

. Tailwater fisheries may be created at the outflow from large dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

s, where the size of the reservoir creates a steep temperature gradient, with colder water stored at the bottom of the reservoir near the outlet. The constant cold-water flow provided by the reservoir's outflow, coupled with the generally silt-free nature of the outflow, creates ideal water conditions for cold-water fish such as trout in environments that ordinarily might not support a robust trout population. An example of this phenomenon is the fishery at Lee's Ferry

Lee's Ferry

Lee's Ferry is a site on the Colorado River in Coconino County, Arizona, United States, about 7.5 miles southwest of the town of Page, Arizona and the Glen Canyon Dam, and about 9 mi south of the Utah-Arizona border. It is the former location of a ferry established by John D. Lee, a Mormon...

 on the Colorado River

Colorado River

The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...

 in Arizona

Arizona

Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

.

Tailwater also refers to surface runoff

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

 resulting from crop irrigation

Irrigation

Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

. Irrigation practices such as flood irrigation

Surface irrigation

Surface irrigation is defined as the group of application techniques where water is applied and distributed over the soil surface by gravity. It is by far the most common form of irrigation throughout the world and has been practiced in many areas virtually unchanged for thousands of years.Surface...

 and sprinkler irrigation can result in applied water in excess of the infiltration rate

Water cycle

The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...

 of the soil. Sloped fields can allow for the excess water to run off the field, and discharge to a drainage channel or natural water body. Tailwater can carry pollutants such as silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

, nutrients (from fertilizers), and pesticides.