Sorry for such a late post! The image to the left is a picture from Crater Lake, Oregon, is the deepest lake in the United States, the seventh deepest in the world. This lake was formed when the volcano, Mount Mazama, erupted, causing the mountain to collapse onto itself and settling in the lava chamber below. The hole was then filled with spring water, rain and melting snow, which slowly seeps through the bottom of the lake close to the northern portion of the lake. The deep blue color is a result of light entering the lake as it gets absorbed by the water, only reflecting back the deepest blue. Red, orange, yellow, and green are absorbed first as sunlight enters the lake. The depth of the lake only adds to the blue color that we see. The lake is a closed ecosystem, as no stream runs into or out of the lake, and so all fish have been introduced at one point in time.