The victim was identified as Jennifer Karren, 35, according to the Baja California Sur Prosecutor General's Office.
Karren is a Canadian from Calgary, Alberta, according to the Canadian Broadcasting Corporation.
Two other people aboard the Cabo Adventures' vessel were injured in the incident that happened Wednesday a quarter-mile from the Bay of Santa Maria, the Mexican Federal Attorney General's Office for the Protection of the Environment said.
That federal agency is investigating the incident, it said.
The inflatable boat, called the Cabo Adventure 9 and designed for recreational diving, was carrying nine people and was returning from a snorkel tour when a side of the craft collided with the whale, authorities said.
The skipper, José Salazar Tendis, tried to avoid the whale, officials said.
Salazar couldn't be immediately reached for comment.
Karren fell in the water, and a tour guide and another passenger jumped in and brought her back on the boat, the federal agency said.
The vessel captain immediately informed naval rescue officials, and the boat returned to shore as first aid and mouth-to-mouth resuscitation were performed on Karren, the federal agency said. A tourist aboard the watercraft who was also a nurse performed CPR, authorities said.
The Canadian woman was rushed to a hospital, where she was pronounced dead, according to the Baja California Sur Prosecutor General's Office.
The tour company's general director, Felipe Diez-Canedo, released a statement through Mexican authorities
that expressed regret that one of its guests died, despite receiving first aid and being transported to the hospital.