Short answer
A lake is a body of standing water in a basin, usually understood as naturally formed. A reservoir is stored water, often a human-made lake behind a dam. Some natural lakes are regulated or enlarged, so the categories overlap in practice. 1 2
A reservoir may look and function like a lake, but the term usually emphasizes engineered storage or management.
On this page
At a glance
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| Question | Lake | Reservoir |
|---|---|---|
| Usual origin | Natural basin | Engineered impoundment |
| Usual management | May be unmanaged | Often controlled for supply, power or floods |
| Water body | Standing surface water | Standing surface water |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Lake. A standing body of water collected in a basin, commonly formed by natural processes. 1
Reservoir. A body of stored water, commonly an artificial lake formed or controlled by a dam for human purposes. 2
Key differences
USGS describes reservoirs as manmade lakes in common usage. “Reservoir” highlights storage and operational control, while “lake” describes the water body. Naming is not fully standardized: a reservoir can have “Lake” in its proper name. 1 2
How to tell them apart
Find out how the basin formed and whether a dam or control structure maintains it. A glacial basin is a natural lake; water pooled behind Hoover Dam is a reservoir, even though it is called Lake Mead. 1 2
Where they overlap
Both can stratify, support fisheries, receive runoff and lose water by evaporation. Water quality and ecology can be similar despite different origins. 1 2
Edge cases
A natural lake raised by a dam becomes partly managed as a reservoir. Artificial mining pits can form lakes without functioning as water-storage reservoirs. 1 2
Why the distinction exists
Water managers need a word for stored, controllable supply, while geographers and ecologists also need the broader physical term for standing inland water. 1 2
Common misconceptions
The presence of “Lake” on a map does not prove the water body is natural. 1 2
Examples
Lake Superior is a natural lake; Lake Mead is the reservoir impounded by Hoover Dam. 1 2
Sources
Sources checked October 3, 2026.
- U.S. Geological Survey — Lakes and Reservoirs. Lakes overview.
- USGS — EarthWord – Reservoir. Reservoir definition.