Why Lake Waters Are Well Oxygenated at All Depthes in Spring and Autumn?
The main reason that lake waters are so well oxygenated at all depths in the spring and autumn is that the temperatures in the lakes become all the same or uniform.
1 Additional Answer
The reason that lake waters are well oxygenated at all depths in spring and autumn is became of plankton. These times of year see a lot of movement by these organisms. They help to distribute oxygen in the water.