Summer thunderstorms present a severe hazard, especially for those enjoying water activities in pools, lakes, or oceans. Lightning is dangerous, and its electrical energy can travel surprisingly far from the point of strike. Safety during severe weather requires adherence to established guidelines. Understanding the risks specific to water environments is the first step toward safeguarding yourself and others.
Why Lightning Strikes Near Water Are Dangerous
Lightning is a massive electrical discharge seeking the path of least resistance to the ground. When a bolt strikes water, the energy does not necessarily penetrate deep below the surface. Instead, the electrical current disperses rapidly and horizontally across the water’s surface, creating a wide danger zone. This surface-level conductivity is what puts swimmers at high risk, even if the strike occurs some distance away.
The danger extends beyond the immediate strike area because of a phenomenon known as ground current and step potential. Water, and the ground surrounding it, acts as a conductor, carrying the electrical charge outward from the strike point. If a person is standing near the water’s edge, the difference in electrical potential between their two feet can cause the current to travel up one leg and down the other.
This is known as step voltage, and it can be lethal, causing severe muscle contractions or cardiac arrest. Pool structures, which contain underground pipes, metal ladders, and electrical wiring, can also conduct the charge from a distant strike. Consequently, both natural bodies of water and constructed pools pose a significant threat during a storm.
Recognizing the Danger Signal
If you hear thunder, lightning is close enough to strike you. Lightning can strike as far as 10 miles away from the rain area in a thunderstorm, and it is the first hazard to arrive and the last to leave. Therefore, any audible thunder is the signal to evacuate the water and seek safe shelter immediately.
The “Flash-to-Bang” method offers a practical way to estimate the storm’s proximity, though it should never delay action. To use this method, you count the number of seconds between seeing the lightning flash and hearing the corresponding thunder. Dividing that count by five provides a rough estimate of the storm’s distance in miles. If the time between the flash and the bang is 30 seconds or less, the storm is approximately six miles away, and you must clear the area without delay.
The Standard Waiting Period
The standard rule for returning to water activities after a thunderstorm is to wait a full 30 minutes. This waiting period begins only after the last sound of thunder is heard or the last flash of lightning is seen. This duration ensures the entire storm cell has moved far enough away to eliminate the risk of a late or “bolt from the blue” strike.
The 30-minute countdown must be reset to zero every single time thunder is heard or lightning is observed. Thunderstorms frequently move slowly or cycle, and a storm that seemed to be passing can easily intensify or change direction. This strict adherence to the reset rule is what makes the protocol effective in managing the continuing hazard.
Waiting until the storm is at least 10 to 12 miles away significantly reduces the risk of a strike. Since a typical storm travels at around 25 miles per hour, the 30-minute delay allows it to travel a considerable distance. Returning early increases the chance of being struck by lightning from the trailing edge of the storm.
Defining Safe Shelter During a Storm
Once you have evacuated the water, move to a location that provides protection while you wait out the 30-minute period. A safe shelter is a fully enclosed, substantial building that contains plumbing or electrical wiring. These internal systems offer a path for the electrical current to safely ground itself if the structure is struck.
If a permanent building is unavailable, an enclosed hard-topped metal vehicle with the windows rolled up serves as an alternative. The metal frame of the vehicle directs the electrical current around the passengers and into the ground. Unsafe locations include small, open-sided structures like picnic shelters, covered porches, sheds, or gazebos, as these lack the necessary grounding infrastructure.