Three quick-thinking Mandurah teenagers saved the life of a stranded baby dolphin on Thursday afternoon.

While kayaking on Goegrup Lake on the Serpentine River, Zachary Allegretta, Michael Randall and Ryan Dalzell, all 15 years old, saw the calf in distress and didn't think twice about rushing to its aid.

"We thought it was sick at first, so we got close to it and we saw the tide was going out and it was beached," Zachary said.

"The mother wasn't anywhere around and the baby was doing its mimic call to attract her."