Glossary of stream, lake and watershed terms
Kings Co., Wahington, USA

A Glossary of Some Common Terms Used Around Lakes
University of Wisconsin-Stevens Point

Water on the Web

Glossary of General Wetland and Watershed Terms
Association of State Wetland Managers (USA)

From Springer 

Athalassohaline: Having a salt composition very different from that of seawater

Chemocline: Water layer with steep gradients of concentrations of chemicals (nutrients, oxygen, salts, etc.)

Epilimnion: The upper, mixed layer of a stratified lake

Holomixis: Period of complete mixing of a lake with water circulation from top to bottom Hypolimnion: The lower water layer of a stratified lake

Meromixis: Permanent stratification, in which the water layers of a lake do not mix at any time during the annual cycle

Metalimnion: Intermediate layer between the epilimnion and the hypolimnion; often corresponding to the chemocline and/or pycnocline

Mixolimnion: The upper mixed layer of a meromictic lake

Monomixis: Regime in which a seasonally stratified lake turns over once each year

Monimolimnion: The stagnant bottom layer of a meromictic lake

Oxycline: Water layer with a steep oxygen concentration gradient

Pycnocline: Water layer with a steep density (salinity) gradient

Thalassohaline: Having a salt composition similar to that of seawater Thermocline: Water layer with a steep temperature gradient