The body of a man who dived into a lake to try to save two children who got into difficulties has been recovered by police divers.

The 34-year-old Cranbourne West man disappeared as he tried to reach a girl, 11, and a boy 12, whose dinghy became stuck in reeds on Lysterfield Lake in Melbourne's southeast.

Despite the efforts of two other men to help him, he disappeared under the water about 4pm (AEDT) on Sunday.

Police divers recovered his body at 8.40pm.