The Great Lakes do have tides, but at the same time, the five lakes are considered non-tidal. Confused? Here’s what that means: The moon’s gravitational pull on the earth does indeed affect the water in the Great Lakes in the same way that it does the oceans, according to the National Ocean Service, including twice-daily ebbs and flows such as you would see at the shore of the ocean. However, the effect is downright trivial. When the tides there are at their highest — during the Great Lakes Spring Tide — the combined forces of the sun and moon exert the biggest pull on the lakes but the difference is only a couple of inches. What causes a significantly more dramatic effect on the lakes’ water levels are more mundane things like barometric pressure and the wind. As such, that means that the Great Lakes are considered non-tidal.

However, that’s not the end of the story. The lakes are also subject to an effect of the wind that creates an oscillating wave that has a lifespan of a few hours, not unlike a tide. This phenomenon, called a “seiche,” is often mistaken for a tide.