The current across the whole lake, hour by hour, from NOAA's forecast model. Tap the water for its speed.
This is a forecast model, not a measurement. NOAA runs the Lake Michigan and Huron Operational Forecast System four times a day. It divides the two lakes into 171,377 triangles, from about 200 m across near shore to 3.5 km in the middle, stacks 20 layers of water in each one, and pushes them with the wind, the rivers and the water level.
The page reads two of those layers straight from NOAA's files: the top twentieth of the water and the bottom twentieth. The last 12 hours come from runs driven by observed weather. The next 48 are the forecast. A new run arrives about every six hours. To load on a phone, the page keeps about 16,000 points of the model's mesh: all of the open lake, and a thinned copy of the fine triangles along the shore.
Wind does almost all of it. Lake Michigan has no big river running through it. Its only natural way out is the Straits of Mackinac, where the water sloshes back and forth between Michigan and Huron, so it would take about 99 years to replace the water.
Michigan and Huron sit at the same level and are really one lake, so NOAA models them together. This page shows the Michigan half, as far as the Mackinac Bridge. A few harbours and river mouths have no colour because the model leaves them out. Line speed on screen is exaggerated in slow water so you can see it move. East of the bridge, the Lake Huron map picks up.