I've read a little bit talking about how the muskies run upstream in the spring and the fall and can be concentrated in areas like dams due to the obstruction. I agree with Red that it's for the increase in water temperatures but also increased dissolved oxygen, and baitfished get stacked there too. Very similar to smaller creeks entering, these seem to be rest areas for fish during these times. I enjoy fishing through the whole year, especially this time of the year. Something about being in fresh snow with green water to the top of the banks, and seeing fish come out of it following your lure right up towards your rod tip...and WHAM!! It's a beautiful thing!! I had two follows Saturday by muskies in the 30" range and caught a fat 32" pike on my newest color pattern, the carpsucker.