Here's how Ted Swift and his associates describe the optical effects of particles and algae in the lake. Pure water absorbs light in the red portion of the spectrum, and scatters very little light. The result is a bright blue color. Mineral particles scatter more blue light than red. So sediment laden water appears reddish-brown.
Algal particles scatter some light, but mostly they strongly absorb red and blue light.
This is because algae grow by absorbing light and carbon dioxide and producing green chlorophyll. As you might expect, chlorophyll makes water appear green. Swift pointed out that light penetrates to 105 meters, and possibly deeper, so algae can and do grow at great depths in the lake. He also explains that tiny mineral particles settle slowly, and some are mixed back up in winter. So, a fraction of particles washed into the lake each year is still around when a fresh batch moves in during the next snowmelt.