Littoral zoneNear shore, where sunlight reaches the bottom and rooted plants grow.
Limnetic zoneOpen, sunlit water away from shore, home to plankton and fish.
Profundal zoneDeep water that little light reaches; colder and denser.
Benthic zoneThe bottom sediment, where insect larvae and small crustaceans live.
Summer layers 3
EpilimnionThe upper, warm layer, kept well mixed by the wind.
Metalimnion (thermocline)The middle layer, where temperature drops quickly with depth.
HypolimnionThe bottom layer of colder, denser water.
Water in, water out, the shore 3
InflowWater flowing into the lake.
OutflowWater flowing out of the lake, often as a river or stream.
ShorelineWhere the lake and the land meet.
How this list was compiled: Every name checked on 2026-09-30 in at least two of these. (1) Water on the Web, University of Minnesota Duluth, Lake Ecology: Lake Zones, Density Stratification and the glossary, https://www.waterontheweb.org/under/lakeecology/10_biological_lakezones.html (littoral, limnetic and benthic zones; epilimnion, metalimnion or thermocline, hypolimnion; inflow, outflow, shoreline). (2) University of California Museum of Paleontology, The freshwater biome, https://ucmp.berkeley.edu/exhibits/biomes/freshwater.php (littoral, limnetic and profundal zones, thermocline, shoreline). (3) USGS Water Science School, Lakes and Reservoirs, https://www.usgs.gov/special-topics/water-science-school/science/lakes-and-reservoirs (inflows and outflows). (4) Wikipedia, Lake ecosystem; Lake stratification; Lake; Limnetic zone; Profundal zone, https://en.wikipedia.org/wiki/Lake_ecosystem. (5) National Geographic Education, Lake, https://education.nationalgeographic.org/resource/lake/ (epilimnion, metalimnion or thermocline, hypolimnion; open lakes have an outlet). Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry. Own original drawing; nothing is traced or copied. Licence: own work
How it works
The parts of a lake are named two ways. The first drawing splits it by light and depth into four zones. The second splits the same water by summer temperature into three layers.
Read the full guide
Zones: follow the light
Where sunlight reaches the bottom and rooted plants grow, the water is the littoral zone. Farther out, the lit open water is the limnetic zone, and the dark water under it is the profundal zone. The sediment under all of it is the benthic zone.
Layers: follow the temperature
In summer a deep lake settles into a warm, wind-mixed epilimnion on top, a cold hypolimnion at the bottom and a metalimnion between them where the temperature drops quickly. In spring and fall the layers mix, which is called turnover.
Questions and answers
What are the zones of a lake?
The littoral zone is the shallow water near shore, the limnetic zone the sunlit open water, and the profundal zone the dark water below it. The benthic zone is the bottom sediment.
What are the three layers of a lake?
The epilimnion on top, the metalimnion in the middle and the hypolimnion at the bottom. They form in summer because warm water is lighter than cold water and floats on it.
Is the thermocline the same as the metalimnion?
The two words are often used for the same middle layer. Strictly, the thermocline is the depth inside the metalimnion where the temperature changes fastest. This page takes either answer.
Does every lake have an outflow?
No. National Geographic calls a lake open if water leaves by a river or other outlet, and closed if water leaves only by evaporation. Closed lakes usually turn salty.