Check out that one with the lakes levels over the years. Look closely at 1936, 1966 and now, if the trends repeat again, 2006? Then back to higher levels? If thats what going to happen, we are in for lower levels still for a couple more years. I have heard tales that its a 40 year cycle.
I'm thinking they released some sort of tracking buoys to see the current in the lake. Someone posted another link a while back that was similar and it showed different flow pattens along the St. Clair River and I think it had the Detroit river too. Same kind of deal where they released buoys and tracked them, but with just a chart of the rivers. I really like the pic of the lake in the first one though.