You can see the rocks clearly resting on the bottom. The lake is in its natural, pristine state. Unclouded and accurately reflecting the image of the world. Later in the day, if you were to return to that same lake, it might not be so serene and reflective. Wind, boats and swimmers are disturbing the surface and distorting what is reflected.
Silt floats in the water, clouding it and making it impossible to see the bottom.
Our minds are very much like the lake. When they are still, they are more accurately reflective of reality. But most of the time, our minds are disturbed with activities of daily living which disrupt the clarity of our awareness of reality. They are filled with emotional disruption which clouds our perceptions. Here are some symptoms.