From June to November, humpback whales migrate through the Mozambique Channel on their annual journey between Antarctic feeding grounds and warmer breeding waters. Tofo Bay sits directly in their path, and sightings from shore and from dive boats are common throughout this period. At peak season (August to October), it is unusual to spend a day on the water without seeing at least one.
Dive boats often encounter whales during regular excursions, and some operators run dedicated whale-watching trips. In good conditions you may hear the whales before you see them — their calls carry considerable distances underwater and can sometimes be heard by divers even when the animals themselves are out of sight. Humpbacks are occasionally curious about boats and will approach of their own accord. No guaranteed sightings, obviously, but the odds are very good in the right months.