SAN DIEGO (CBS 8) - Three people are safe Sunday after the small rental boat they were on caught fire in the middle of Mission Bay this afternoon.

The three passengers got off the boat safely and were picked up by good Samaritans on the water. When lifeguards arrived, they found a fully engulfed rental boat.

Lifeguards say boat fires can be extremely dangerous to control.

"We try to take as much precaution as we can, but there are some elements of a boat fire that we need to be very aware of. For example, if there's fuel on board a boat we need to make sure that fuel doesn't explode when we're in close proximity," said Lt. Andy Lerum, SD Lifeguards.

The cause of the fire is under investigation.