Changing seasons – stratification and the turnover

Changing seasons – stratification and the turnover

During this turnover there is a lot going on chemically too. As the bottom waters are forced up, they bring with them all sorts of organic material that has been sinking all year long. You often see this as lines what looks like grass clippings or debris on the surface. But because the water near the bottom had little oxygen, this muck has not been decomposing. Lakes often have a peculiar smell during turnover because decomposition produces sulfur compounds that stink.

As this organic-rich bottom water is pushed upwards it mixes with oxygen-rich water and very rapid decomposition can occur. This can use up oxygen to a point where it is stressful or even fatal to fish in confined areas. Most of the time however, the turnover does not kill fish, but it does stress them. They are disoriented and forced out of their summer routine. 

Fishing often suffers too. After the turnover the fish are often harder to find. They are not squeezed into the upper epilimnion. They can live and feed anywhere. Temperature and oxygen content may be the same from top to bottom. Fish tend to scatter under these conditions.

As fall progresses, schools of baitfish often move up the creeks and feeder streams following plankton blooms that may continue for several weeks because the water is usually a bit warmer and nutrients may still be available. Forage fish simply follow their food supply. And while bass don’t swim long distances out of their home range, they will move off main lake areas into adjacent coves and creeks to follow their food.

Over a short period, these physical and chemical changes settle out and the bass get into more predictable patterns. As the water continues to cool and winter approaches, the system sets up to repeat this natural cycle.

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