Rip Tide and Undertow
You may have heard about the rip tide or undertow before. These are terms that people commonly use to describe dangerous currents. However, since there are no tides in the Great Lakes (needed to form a rip tide) and currents don’t pull a person down under the water (undertow), they are a bit inaccurate. Instead, we call these dangerous currents. Also, most people know that ocean currents can be dangerous, but don’t suspect that there are such strong currents in the Great Lakes.
The Science of Currents
Currents in the Great Lakes can form from any combination of wind, waves, bottom formation, beach slope, water temperature, man-made structures and natural outlets. For example, during rip currents, the water “piles up” between a sandbar and the beach. It has to find a way back out to sea.
After the pressure builds up, the water creates a pathway and gushes from the shore back out to open water. That’s a rip current; a narrow but powerful stream of water and sand moving (ripping) swiftly away from shore. Rip currents vary in size and speed and can be found on many beaches every day.
In the Great Lakes, there are permanent currents and variable currents. Permanent currents are always found in certain locations — and only vary in strength. For example, strong currents are always present along piers and breakwalls, and can be found where rivers and streams empty into the lake.
Other currents can be more variable, dependent upon the bathymetry (shape of the lake bottom) and the wind and wave conditions. The location and strength of variable currents is difficult to predict, but check the National Weather Service’s Great Lakes Beach Hazard page for up-to-date warnings during the swimming season.
Dangerous current-related incidents in the Great Lakes have occurred when:
- Wind is blowing toward the shore, at 25 mph or less.
- Wave height of 3 to 6 feet.
- Passage of a cold front.
People may feel comfortable swimming with these moderate wind speeds, moderate wave heights, and incoming cold fronts, but these are the conditions which cause dangerous currents to form. Keep these statistics in mind when visiting a beach during blustery weather.
(Source: National Weather Service – Marquette Office)
Dangerous Currents at a Glance:
- Dangerous currents occur in many ocean and Great Lakes beach areas.
- The highest number of deaths and rescues happen in Michigan, specifically along the eastern shore of Lake Michigan.
- Deaths have also occurred along Lake Michigan beaches in Illinois, Indiana and Wisconsin; along Lake Superior beaches in Michigan and Minnesota; and along Lake Erie beaches in Ohio.
- Swimmers near structures are more likely to die.
- Dangerous currents can exceed 5 mph — faster than an Olympic swimmer can swim (2 mph and faster are considered dangerous).
Classroom Lessons and Activities
The Great Lakes Current Incident Database contains information about dangerous currents and current-related drownings or rescues, going back to 2002.
Types of currents
In the Great Lakes, swimmers are most likely to encounter one of five common currents: rip; outlet (river channel); longshore; channel and structural. Flip through the visual gallery of diagrams below.