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The Restless Lake

Two days of surface currents on Lake Ontario, September 20 to 22, 2026, from Environment and Climate Change Canada's Water Cycle Prediction System. Every streak follows the modelled current and its colour shows the true speed. Modelled currents, not direct measurements.

Lake Ontario surface currents at 0.5 m depth, every 2 hours from September 20, 8 a.m. to September 22, 8 a.m. EDT. Data: Environment and Climate Change Canada, Water Cycle Prediction System (WCPS 3.4.0), MSC Datamart, Open Government Licence - Canada. Shoreline and places: Natural Earth (public domain).

23.0 cm/s

lake-wide average current at its peak, Sep 21, 8 a.m. EDT

1.6x

the peak against the low of 14.1 cm/s

63.8 cm/s

fastest water in the window (2.3 km/h), in the west basin

25

model frames, 2 hours apart, over 48 hours

What the data reveals

TWO SURGES

The whole lake speeds up and settles

Lake-wide, the average surface current peaked at 23.0 cm/s at Sep 21, 8 a.m. EDT, 1.6 times its low of 14.1 cm/s (Sep 20, 8 a.m. EDT). The timeline marks the first surge, the lull and the second surge.

THE WEST BASIN

The fastest water runs past Toronto

Fastest water in the window: the west basin, up to 63.8 cm/s (2.3 km/h) at Sep 21, 6 a.m. EDT.

THE NIAGARA RIVER MOUTH

The river keeps pushing north

Right at the Niagara River mouth (the 4 grid cells within 3 km), the surface water heads north in all 25 frames, between north-northwest and north-northeast, at an average 15.8 cm/s.

THE WIND

Switch on the wind that drove it

"Show the wind" lays the same 48 hours of modelled 10 m wind from the companion piece, Wind Over the Lakes, over the currents, so you can see the weather behind each surge.

INTERACTIVE

How to explore it

Three ways to see the water

Flow animates the streaks, Speed shades the lake by current speed, and Streamlines draws the paths as still lines.

Scrub through two days

Drag the timeline or press Play. Markers jump to the first surge, the lull and the second surge. Choose 1x, 2x or 4x.

Show the wind

Turn on the modelled wind for the same hours to see what pushed the water.

Read any spot

Hover or tap the water for speed in cm/s and km/h, the direction in words, and the zone. Drag the cards out of the way.

Zoom and pan

Ctrl and scroll, pinch, or the + and - buttons. Reset view puts everything back.

Keyboard and table

Arrow keys move a probe across the lake with each reading announced. The Table and CSV give every zone, every frame.

About the data

Every figure on this page is computed from the data in the visualization, and the visualization says plainly what is measured and what is modelled.

  • Source: Environment and Climate Change Canada, Water Cycle Prediction System (WCPS 3.4.0, the GEM atmospheric model coupled with the NEMO-CICE ocean and ice model), 1 km Great Lakes configuration, MSC Datamart. Open Government Licence - Canada.
  • Model output (a short-range forecast), not measurements. Each 2-hour frame comes from the most recent model run, at forecast hours 2 to 6.
  • Window: September 20, 8 a.m. to September 22, 8 a.m. EDT. A scan of every day from September 9 to October 7 puts September 21 at the top, at 18.8 cm/s (next: September 22 at 18.7 cm/s).
  • Surface currents at 0.5 m depth, regridded from about 0.9 km to 0.025 degrees (about 2 to 3 km) by averaging native water cells: 3,717 water cells.
  • Motion is sped up so it can be seen: time plays 3,600 times faster and particles move 40,000 times faster than the water. Colour is always the true speed.
  • Shoreline and places: Natural Earth (public domain). Not affiliated with or endorsed by Environment and Climate Change Canada.

Have data that moves?

Currents, wind, traffic, shipments or people: we turn flows into maps anyone can explore, with every number traceable to its source. Tell us about your data.

More flows

Above the Falls: the upper Niagara River with pale blue streaks splitting around Grand Island into the Chippawa and Tonawanda channels.

Above the Falls

Upper Niagara River. 5,960 m3/s Lake Erie's average measured outflow at Fort Erie over the 13 days.

See the example

Wind Over the Lakes: Southern Ontario and the lower Great Lakes scattered with streaks that follow the modelled 10 m wind, coloured by speed.

Wind Over the Lakes

Southern Ontario wind. 49 km/h strongest wind in the window, over Lake Erie, Sep 22, 6 a.m. EDT.

See the example

Downtown Pulse: downtown Toronto streets with glowing counted road segments and small dots travelling along them, coloured by measured speed.

Downtown Pulse

Downtown Toronto traffic. 44,591 vehicles an hour across all counted directions at the 5:30 p.m. peak.

See the example