I always heard that the brown tint in all our local Duluth streams is from the high iron content.  Can anyone verify this?

The Nemadji River is a source of a lot of the sediment - some would be transported in the river naturally, but land use changes cause more of the clay to erode. Pollutants can bind to the sediment particles, so it can be bad for the big lake (and the river itself). Good info on the City of Superior website:

http://www.ci.superior.wi.us/index.aspx?NID=365

Brown color (aka root beer color) of north shore streams is related to tannin in the water (from plants) vs iron.

It is quite common after a big rain to see the stripe of brown in the lake at various river mouths, especially from south shore streams with more clay soils in their river beds.

Barb and I were invited for a cruise on the Blue Heron (UMD research vessel) yesterday and we learned that the brown color does in fact come primarily from the Nemadji and that UMD has a research project going about the effect of sulfates on wild rice.

Lake Michigan has more algae than in the past. I drove along the shore and all the rocks are just coated. I am guessing it's the warmer, shallow waters and perhaps climate change. We are much warmer during the past few summers. Lake water temps are higher than average. None of it is good for the Great Lakes.

@Bob, I'm assuming that you're grossly exaggerating intentionally ... at least spend a few minutes reading the wiki site or other sources about flow rates and residence time ... climate change is real.

The 'chocolate' color in Lake Superior is due to red clay (and silt or 'mud') sediment from the Nemadji River.  The clay is red from iron that is bound up in the clay.  The reason there's so much clay in the lake right now is the torrential rain that washed out several bridges in the Nemadji river basin last Tuesday, contributing a greater sediment load to the lake than normal.  The Nemadji flows through mostly clay, so strong rain events contribute more clay to the river, and thus the lake. Clay stays in suspension much longer than silt, sand, or gravel, so it'll take awhile to settle out. This is a natural process that will continue essentially forever (or until the next ice age, or the Nemadji basin elevation erodes to the same elevation as the lake).  The St. Louis River does not flow through nearly as much clay so it contributes much less sediment to the lake.

There has been an increase in algae attached to the rocks in Lake Michigan and the other great lakes, largely due to the zebra mussels, which filter so much out of the water that it becomes clearer; this clarity allows more light to penetrate, leading to the growth of this algae attached to the rocks on the bottom.
  
I don't know of any studies showing greater amounts of algae in Lake Superior, though studies have shown greater amounts of algae near stream mouths; no surprise, as the streams bring nutrients into the lake.  Here in Duluth we have the mighty St. Louis, not to mention all the lovely fertilized lawns, sewer overflows, and doggie "treats" left on the ground, all of which are great sources of even more nutrients to help that algae grow.

As to the red color, seems folks have answered that; the Nemadji is a big source of clay; part natural, part due to land cover changes, part still due to destabilized banks created when the entire area was clearcut 100 years or so ago.