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 Erie Operational Forecast System four times a day. It divides the lake into 11,509 triangles, about 100 m across near shore and up to 2.5 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.
Wind does almost all of it. The Detroit River adds water at the west end and the Niagara takes it out at the east, but that flow is slow: it would need about two and a half years to replace the water in the lake.
A few bays have no colour (Sandusky Bay, Rondeau Bay, the marsh behind Long Point, Presque Isle Bay). The model leaves them out. Line speed on screen is exaggerated in slow water so you can see it move. Where the lake ends, the Niagara River map picks up.