My son and I went to one of our lakes a few days ago to let the dogs run, and swim. They love this area, they can be off leash and just be dogs!
From the top of the trail we could see the lake, and I snapped this first photo. The water looked odd. Usually this lake is a sky blue in color when the sun is out. It is crystal clear, the dogs drink from it, there are usually a lot of fish biting. Good for fishing, in fact that is why my son decided to join us. He brought his fishing poles hoping to catch a catfish.
Well, as I said above from a distance something was off. The water wasn’t blue. It was maroon. The camera had a hard time picking up the true color, and I tried everything I knew. The color just wouldn’t come out as red as in real life.
I got scared since we have had a bloom of green algae in the area, and it is very dangerous and toxic. The color of this dangerous algae was the exact same color as our favorite lake spot. I called the dogs to me, and my son held them back away from the water. I walked down to the water’s edge and it dawned on me what I was seeing.
It is called lake turnover. Each spring and fall lakes, if deep enough will turn over. The water from the bottom comes to the top and the water from the top goes to the very bottom.
Here is where the science lesson comes in. I will explain a little bit as we go through the pictures I took.
I hope you enjoy.
Have you ever been swimming in a lake and felt the cool water at your toes? This is called Thermal Stratification. This is when the water in a lake is divided into different layers depending on the temperature. In the summer the water on the top is heated and the cooler water sinks to the bottom.
Lakes begin to stratify due to the difference in air temperature. This happens when the weather gets warmer from the sun. Solar radiation warms the layer on top much faster than the deeper water. In fact, sunlight only penetrates a few meters into the lake, warming just the top few metres.
The middle layer is the transition zone of water between the epilimnion and the bottom cold hypolimnion, called the metalimnion. This layer is a place where the shallowest of cool water gradually warm up until the mix into the epilimnion.
Throughout the summer, wind, and waves cause the water to mix.
The greatest temperature difference is called the thermocline and occures within the metalimnion.
Eventually, the epilimnion warms to the point where the density between the layers is so large that wind and waves no longer generate enough energy to incorporate hypolimnetic water. As summer turns to fall, the surface waters cool and sink, mixing the epilimnion down to the hypolimnion and weakening the thermacline.
Eventually, the epilimnion cools until the entire lake is the same temperature. This allows the lake turnover to occur.