The Elephant Rock Beach Club is a private club in Massachusetts. It’s named after Elephant Rock, a natural formation about 250 feet offshore.

Many members swim out to the rock. One day a guest swam out to the rock, dove off it, and injured herself on a dangerous part of the rock that was submerged just under the water. She sued the club for not warning of the danger.

The club claimed that it couldn’t be held responsible for the accident because it didn’t own the rock. The rock was beyond its property line, in waters owned by the state.

But a federal court said that the club had effectively taken control of the rock, because it had established rules prohibiting small children from using it, and because lifeguards often whistled people away from it on days when there were difficult swimming conditions.

Although the rock wasn’t on the club’s property, the court said landowners sometimes have a legal duty to prevent people from being hurt on a neighboring property. For instance, it pointed to an earlier case where a city was sued for not putting up a fence between a city-owned playground and a railroad track.