I was reading a Cedar River water quality pdf on the DNR website and found this information out about the river below Cedar Rapids. As of 7/24/08.
The staggering volume of water in the Cedar River during the flood diluted the pollution to the point that the concentration of pollutants we found was very small. In fact, many pollutants were not even detected.
Bacteria counts (E. coli, specifically) in the Cedar River were high during the flood and were higher below Cedar Rapids than above. Bacteria counts are still high after the flood and we still see an increase below Cedar Rapids. The levels are similar to bacteria counts that we regularly see after heavy rains in many of Iowa's streams. However, in this case the bacteria counts may be of more concern because of the potential for human pathogens in the sewage is higher than if the bacteria came from soil or animal waste. Elevated bacteria can increase the risk of illness in people that recreate in these streams. The highest risk comes from swallowing the water while swimming or skiing.
Sounds to me like the pollutants are pretty low but bacteria levels are high. If there is risk of coming into contact with human pathogens from the water, count me out.