It's not just you. That lake may smell a little strange.
But that's actually a good thing!
It means nature is doing her job.
Often referred to as seasonal turnover, lake destratification usually occurs each fall and spring. The process is harmless to people, minus the assault on the senses. However, it can affect the health of the fish.
Turnover is essentially the process of a lake's water turning over from top (epilimnion) to bottom (hypolimnion,) according to National Geographic. During the summer, the surface layer is the warmest as it's heated by the sun. The deeper layer is cold as the sun's radiation doesn't reach that dark layer. Once fall arrives, the warm surface water begins to cool, and as it does, it becomes denser, which causes the layer to sink. That dense water forces the layer of water at the bottom to rise or turnover. The process allows for oxygen to be replenished and nutrients to be distributed throughout the lake.
The process typically happens fairly quickly, said Jenna Olson, Brazos River Authority environmental programs coordinator. Often just over a matter of days. Shallow lakes, such as those less than 20 feet deep, stay well mixed throughout the year, preventing it from needing to turnover, Olson said.
When the lake turnover occurs, nutrients and decomposing organic matter from the bottom are mixed throughout the lake, often causing the lake to have an unpleasant smell, according to the University of Nebraska-Lincoln Institute of Agriculture and Natural Resources.
"The onset of fall turnover sometimes produces a sulfurous or rotten-egg odor," according to this article in the Sierra Sun. "It comes from sulfur dioxide gas produced by decomposition during the summer and trapped within the hypolimnion. When the deep water reaches the surface during fall turnover, the sulfur dioxide is released into the atmosphere."
The smell typically lasts throughout the turnover event, which means the offensive odor lingers for just a few days, Olson said. The water could appear muddy throughout the process to anyone along the banks, she said.
The process is pretty stressful to our fish friends, Olson said. Once the layers begin mixing, the good oxygen from the top layer suddenly becomes diluted with the lack of oxygen in the lower level, she said. And if the turnover happens too quickly, the oxygen level can drop low enough to result in a fish kill.
Oxygen is, after all, the key to life.
There's so much happening beneath the surface of your favorite reservoir. Water really is amazing.