High Wave Action on the Great Lakes
Dangerous currents aren't the only hazards swimmers face when swimming in the Great Lakes
Image 1. Great Lakes Waves can quickly become overwhelming to swimmers. Slide modified from a beach hazards presentation by Bob Dukesherer (NWS Grand Rapids, MI)
The Dangers of Swimming in Great Lakes Waves
A quick review of Great Lakes fatality and rescue incidents reveals a common factor: moderate to high waves with a short period. Waves on the Great Lakes are different from the ocean because they are driven by local winds (whereas the ocean contains both locally wind driven waves and waves travelling from far distances-or swell). As a result, they typically have a much shorter Period, or length of time in between each successive wave. This means swimmers have less time to recover from a wave before the next wave hits. This also leads to the waves appearing more chaotic than traditional ocean waves. Some compare the Great Lakes to swimming in a washing mashine because the waves can become so disorganized and choppy (image 3). The data collected on Great Lakes current related incidents shows that most drowning fatalities and rescues occurred when wave heights ranged from 3 to 6 feet (figure 1), and wave periods between 3 and 5 seconds (figure 2).
Figure 1: A majority of current-related incidents occurred during moderate to high wave heights. Most people are not usually confident swimming in waves greater than 6 feet, so the number of incidents diminishes once heights reach greater than 6 feet. Waves greater than 6 feet are extremely hazardous and life threatening to anyone entering the water, regardless of swimming ability. (Data from the GLCID, 2013).
Figure 2: Wave Periods observed during current-related incidents. Most of the rescues and drownings occurred at times when the wave period was between 3 and 5 seconds (GLCID, 2013).
Swimming during times of moderate to high waves presents several risks:
1. Waves are coming toward shore in rapid succession-generally with less than 5 seconds in between waves. This can easily tire a swimmer, and leaves little recovery time for those that get knocked down.
2. Dangerous currents are typically present during moderate to high waves. These currents can quickly take a swimmer into deeper water, where waves are over the swimmers head. They can also prevent swimmers from keeping their feet on the bottom, which can make fighting the quickly approaching waves even more difficult and tiresome. A combination of strong currents and moderate to high waves is life threatening to anyone entering the water.