The Great Lakes and the ocean both present dangers, but the hazards differ significantly based on their unique physical characteristics. The common perception is that the vast, deep ocean is inherently more dangerous due to its size and marine life. However, the Great Lakes pose severe, freshwater-specific risks that are often underestimated by the public. Comparing the two requires a distinction between the ocean’s grand scale and the lakes’ intense, localized volatility.
Comparing Hydrodynamic Threats
The mechanics of water movement create distinct hazards in each body of water. Ocean currents are dominated by long-period swells, which are waves generated by distant storms and spaced far apart, sometimes 10 to 12 seconds between crests. Ocean rip currents are a major cause of death, but they often follow predictable patterns related to tides and coastal topography.
In contrast, the Great Lakes feature short-period, choppy waves created by local wind conditions, frequently hitting every three to five seconds. This relentless, rapid wave action is extremely fatiguing for swimmers and makes recovery difficult if a person is knocked down. Great Lakes rip currents are intensified by structural currents, which are strong flows found alongside man-made structures like piers and breakwalls. These currents combine to create a turbulent, chaotic “washing machine” effect nearly impossible to swim against.
A unique threat in the Great Lakes is the seiche, a standing wave that oscillates in the lake basin. Caused by strong winds or rapid changes in atmospheric pressure, a seiche can cause water levels to drop or rise several feet in just a few hours on opposite ends of a lake. This sudden change can expose vast stretches of lakebed before the water violently surges back in, often accompanied by strong currents.
Rapid Weather Changes and Thermal Hazards
Thermal hazards represent a primary danger of the Great Lakes. Freshwater bodies generally have a much lower average temperature than the world’s oceans. Even in the summer, water temperatures can hover in the 50 to 60 degree Fahrenheit range, especially due to upwelling events that bring deep, cold water to the surface.
Immersion in water below 70°F is hazardous, and temperatures between 50 and 60°F can trigger cold shock. Cold shock leads to an involuntary gasp reflex and hyperventilation. This immediate reaction can cause a person to inhale water and drown almost instantly, even for strong swimmers. The ocean maintains vast expanses of temperate water where this sudden cold shock is not a factor.
The Great Lakes are also prone to rapid and intense weather shifts that can catch boaters off guard. Due to their smaller surface area compared to the ocean, storms can form and intensify locally with great speed, producing violent squalls and sudden increases in wave height. These intense, localized weather events quickly transform a calm day into a life-threatening situation, often with less warning than a large, slow-moving ocean storm.
Biological and Anthropogenic Risks
The ocean’s primary biological hazards are well-known, including the risk from marine megafauna like sharks and various species of venomous jellyfish. The Great Lakes, being freshwater, are free of these large animal threats, but they harbor their own set of biological and human-made dangers. Waterborne pathogens and toxic algal blooms, particularly in shallower lakes like Erie, present a public health risk that can make water unsafe for contact or drinking.
Invasive species pose a more direct physical hazard to recreational users. Quagga and zebra mussels, for instance, form dense colonies with razor-sharp shells that can severely cut swimmers’ feet, necessitating the use of protective footwear on infested beaches.
Beyond biological threats, the density of commercial shipping traffic in the Great Lakes presents a significant navigational hazard. Massive commercial freighters, some over a thousand feet long, share narrow shipping channels with small recreational boats. These large vessels require over a mile to stop and have limited maneuverability, creating a high-stakes collision risk for inexperienced boaters who fail to yield the right-of-way.