Pond Boss Forums INTRO Common Pond Q&A (archives) Bill Cody's definition of thermocline & effect on oxygen loss

Pond stratification stability can change year to year especially as the pond ages. Pond aging (eutrophication) results in usually more plankton growing in the water column. Increased plankton results in decreased water clarity. Decreased or increased water clarity changes how the pond warms in the summer thus clarity and the wind have big affects how the pond warms and where the thermocline forms.

Shallower thermoclines usually means that below is a larger volume of water with low or no dissolved oxygen (larger anoxic zone). Thus a pond that did not previously have fish kills can now have a fish kill. Weather events such as cold rain or hail storms can also play a big role in destratification of ponds. If that bottom water zone was anoxic and large, it can degrade the top water enough to cause fish kills. The most sensitive fish will die first and most tolerant will die last.