Swimming during a thunderstorm is dangerous. Lightning is a powerful electrical discharge, and when it interacts with water, the risks to anyone in or near the water become substantial. The electrical properties of water, combined with the various ways lightning can strike, create a hazardous environment that can lead to severe injury or fatality.
Why Water Amplifies Lightning’s Danger
Water is an efficient conductor of electricity, amplifying lightning’s danger. While pure water is a poor conductor, natural bodies of water contain dissolved salts and impurities that create ions, allowing electricity to flow readily. When lightning strikes a body of water, its immense electrical current, which can reach hundreds of millions of volts, does not penetrate deeply but instead spreads rapidly across the surface in all directions.
Saltwater, due to its higher concentration of dissolved ions, is a better conductor of electricity than freshwater. Despite this difference, both types of water pose a severe risk during a lightning storm. The primary concern is not how deep the current travels, but how widely it disperses across the surface, making a large area electrified. This conductivity means that anyone in contact with the water, even at a distance from the direct strike, can become a part of the electrical path.
Specific Lightning Hazards in Water
A direct strike can occur if a person is the tallest object in the vicinity, making them a direct target for the electrical discharge. However, direct strikes are not the only, or even the most common, way people are injured by lightning in water environments. The electrical current can travel through the water from a strike that occurs on land nearby, a phenomenon known as ground current.
Another hazard is a side flash, where lightning strikes a taller object, such as a tree or a building, and a portion of the electrical current jumps or “splashes” from that object to a nearby person. This can occur even if the person is not directly touching the struck object but is within close proximity. Additionally, step voltage arises when lightning strikes the ground or water, creating a voltage difference between two points on the surface. If a person’s feet are at different points within this electrified area, a current can flow through their body, potentially causing severe injury.
Staying Safe During a Thunderstorm
The most important action is to exit the water immediately at the first sign of thunder or lightning. Thunder indicates that lightning is close enough to strike, even if the storm appears distant. This immediate evacuation applies to all bodies of water, including pools, lakes, rivers, and oceans.
Once out of the water, seek safe shelter as quickly as possible. The safest places are fully enclosed buildings with plumbing or electrical wiring, or a hard-topped, enclosed vehicle. Structures like picnic shelters, gazebos, or isolated trees offer inadequate protection and should be avoided, as they can attract lightning or provide little shielding from its effects. It is important to remain in safe shelter for at least 30 minutes after the last clap of thunder is heard or the last lightning flash is seen. This “30-30 rule” helps ensure the storm has passed and reduces the risk of returning to outdoor activities too soon.