The Great Lakes are five vast inland seas. Lake Superior, the largest, is approximately the same size as Iceland. Taken together, almost two Englands could fit inside the total surface area of the lakes. They’re big. Because they’re contained within smaller basins they don’t have tides like you’d see on the oceans, although the Great Lakes tides are measurable. A significant tide-like event that occurs on the Great Lakes is called a seiche, which is a sloshing of water caused by air pressure or wind. A seiche typically occurs quickly and can drop or raise the water significantly; some seiches are reported to have changed the water levels by 12 to 15 feet within 30 minutes and others came on so fast that they washed fishermen away. The large seiches occur every once in awhile, but small seiches almost occur constantly. If you kayak on the Great Lakes long enough, eventually you’ll witness a seiche.
The first seiche that I witnessed was several feet tall. I had just finished guiding a kayak tour and was heading to lunch when I noticed some standing waves forming in the mouth of the river. There wasn’t any waves or wind on Lake Superior, so I though it was odd. After lunch, I walked back to the boats to get ready for the next tour when I noticed that the water level in the river looked higher. A small sand island was completely submerged. Thirty minutes later the island rose above the water again. Later in the day, I heard a news report that a seiche of similar height had occurred at about the same time almost 150 miles across the lake.
The next time I experienced a seiche was in Big Bay, Michigan. We were practicing rescues and skills in a harbor. Someone noticed a current pushing into the harbor and we watched the water level rise by 6 to 10 inches. Then it rushed out. Then it rushed back in. It did this over the next hour or so with the periods between high water and low water averaging about 20 minutes.
After that experience, I tried to watch out for more seiches. In 2011, I spent 45 days kayaking 800 miles on the Great Lakes and I had a camera ready to capture any seiches. I experienced three that I caught on camera. Two were small. The third one was hard to gage.
The first was on Lake Huron. I was in camp and noticed the water level going up even though the lake was mirror calm. Over a half hour it raised several inches.
The next was on Lake Superior near Sault Ste. Marie. So much water went out that I couldn’t really figure out the height, but it was enough to make me have to drag my kayak to the beach which was normally submerged.
During the third I felt my kayak getting pushed along by a current and then it felt like the current stopped. I landed on a rocky point and watched water drain out from under my kayak. About 30 minutes later the water came back. In the third picture you can see some ripples formed by the water rushing back in.
A related event on the Great Lakes is a storm surge. The picture below I took during the Extratropical Cyclone of October 2010. Look at how the breakwall on the right-hand side of the photo is inundated by water. That breakwall is typically five to six feet above the water level. Usually, the opposite side of the lake drops by as much.
While the Great Lakes might not have the constant tides and tidal currents of the oceans, there’s still plenty of interesting events to keep a kayaker happy.