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Coast · 6 min read

Mafia Island whale sharks: the season, the rules and the odds

The season, the rules, and why it is not a guarantee.

Active Kili Top · Arusha · Updated 3 October 2026
A whale shark swimming through deep blue water
A whale shark, the largest fish in the sea.

The Mafia Island whale sharks are the reason most people have heard of the island at all. Each year, from about October to March, young whale sharks feed at the surface a short boat ride from Kilindoni, the island’s small main town, and visitors can snorkel beside them. It is one of the few places on the East African coast where this happens dependably.

Dependably is not the same as certainly. This guide covers when the sharks are usually seen and why, where the trips go, the rules in the water, and what a careful traveller should expect on the day. For the island itself, its lodges and its diving, see our Mafia Island page.

The short answer

Whale sharks feed at the surface off Kilindoni, on the west coast of Mafia Island, from about October to March, with the most sightings from November to February. You snorkel with them from a boat. Scuba and touching are not allowed, and no operator can guarantee a sighting on a given day.

At a glance: the Mafia Island whale sharks through the year

Tagged sharks stay near Mafia all year, but outside the season they feed deeper and further offshore.
MonthsWhale sharksWhat to expect
October and NovemberSightings begin and buildClearer water, fewer sharks on some days, short rains in November
December to FebruaryThe most sightingsHot and calm; the water is thick with plankton, so less clear
MarchThinning outHumid, with rain building late in the month
April and MayNot a seasonLong rains, rough sea, most lodges closed
June to SeptemberRarely seen at the surfaceDry and breezy; good diving inside Chole Bay
Next: The season ↓Contents ↑

Whale shark season on Mafia Island: October to March

The season runs from about October to March. Researchers who have studied the sharks for years put the main sighting period at October to February, and local operators generally run trips into March while the animals are still being found. Within that, mid-December to late January tends to bring the most sharks. October and November bring fewer, in clearer water.

The reason is food. Mafia lies about 20 kilometres off the delta of the Rufiji, Tanzania’s largest river, which carries nutrients into the shallow sea on the island’s western side. In the hot months, north-easterly winds help concentrate dense patches of tiny shrimp and other plankton near the surface. The sharks come up to feed on them, mouths open, moving slowly, and that is when a snorkeller can keep up.

From April the long rains arrive, the sea turns rough and most lodges on the island close until June. Between June and September the island is open and pleasant, and the diving inside Chole Bay is good, but whale sharks are seldom seen at the surface. If the sharks are the purpose of the trip, do not book those months and hope.

Next: Where they are ↓Contents ↑

Where the whale sharks are: Kilindoni, outside the marine park

The sharks are seen in Kilindoni Bay, on the sheltered western side of the island facing the mainland. Boats leave from the beach at Kilindoni, usually in the morning, and the search area is close inshore. A study published in 2020 found that the core summer feeding area covers only about 23 square kilometres, which is why searches here are short compared with most places.

One detail surprises people. Mafia Island Marine Park, Tanzania’s first marine park, was set up in the mid-1990s and protects Chole Bay and the reefs of the south and east. The whale sharks’ core area on the west side lies outside its boundary. The marine park fee belongs to staying and diving inside the park, and the sharks themselves have no park protection where they feed.

The animals are mostly juveniles. In the same study the sharks measured between four and nine metres, with a median of about six, and nearly nine in ten were male. Around 200 individuals have been identified from the spot patterns on their flanks. Whale sharks are the largest fish in the sea and are classed as Endangered on the IUCN Red List.

Next: The rules ↓Contents ↑

Swimming with whale sharks: the code of conduct

You snorkel. Scuba diving with the whale sharks is not allowed, and it would be pointless anyway, because the animals feed at the surface. Trips go out in wooden boats with a guide and a spotter. When a shark is found, the boat stops well short of it and swimmers slip into the water quietly, in small groups, with a guide.

A code of conduct for these trips was drawn up with conservation groups, among them the Marine Megafauna Foundation, Sea Sense and WWF, and is used by lodges and boats across the island. As published, it asks swimmers to stay at least three metres from the shark and never in front of its mouth, and it allows no touching, no riding and no flash. No more than ten swimmers may be with one shark, and one boat at a time near it.

The code is only as good as the crew that follows it. Before you book, ask how many people the boat carries, whether a guide enters the water with you, and what happens when several boats find the same shark. A crew that drops swimmers on top of the animal, or motors after it when it dives, is doing what the code exists to stop. Wear a rash vest in place of sunscreen where you can.

Next: Not a guarantee ↓Contents ↑

Why a whale shark sighting is not guaranteed

No honest operator will promise a whale shark. They are wild animals, feeding where the plankton happens to be that morning. In the middle of the season the odds on any one trip are good, and most visitors who stay several days do see them, but there are blank mornings, and days when wind or rain keeps the boats on the beach.

It also helps to know what a good day looks like. The water that feeds the sharks is green and soupy, so do not expect reef clarity. You may see a wide mouth and a spotted back passing a few metres away and then have to swim hard to stay alongside. Some encounters last many minutes. Others are a single pass. You need to be at ease in deep, open water.

The tagging work explains the off season. Acoustic tags showed that many of Mafia’s sharks do not migrate away at all. They remain near the island throughout the year, but from about March to September they feed deeper and further from shore, out of sight of the boats. So the season is a matter of where the food is, and it moves a little from year to year.

Next: Planning the trip ↓Contents ↑

How to get to Mafia Island, and how long to stay

Mafia is reached by light aircraft. The flight from Dar es Salaam takes about half an hour, and there are flights from Zanzibar and, less often, from the airstrips of Nyerere National Park. Bags are limited, usually to around 15 kg in soft luggage. The airstrip is at Kilindoni, a few minutes from where the whale shark boats leave.

Stay at least three nights in season, and four if you can. That gives two or three mornings on the water, which is the practical answer to an animal nobody can schedule. Most lodges are on Chole Bay, inside the marine park, a short drive across the island from Kilindoni. At the time of writing (October 2026), lodges there quote a park fee of USD 23.60 per person per day. Ask for the current figure when you book.

Mafia pairs naturally with a southern safari, because the same river feeds both. Our Nyerere by Boat and on Foot plan ends a short flight away, and Ruaha and Nyerere can finish the same way. From the north, Mafia can follow a few nights on Zanzibar. If you are weighing the islands, read Pemba or Zanzibar as well.

Next: Questions ↓Contents ↑

Questions people ask

From about October to March, with the most sightings between November and February. October and November often have clearer water and fewer sharks. December to February has more sharks in murkier, plankton-rich water. April and May are the long rains, when most lodges close.

No. In season the chances are good, and a stay of three or four nights gives several mornings to try, but whale sharks are wild animals that follow their food. Wind, rain and the movement of the plankton all produce days with no sighting.

No. Encounters are by snorkel only, from a boat, with a guide. The sharks feed at the surface, so scuba equipment adds nothing, and the local code of conduct does not allow it. Diving on Mafia happens separately, mostly inside Chole Bay on the other side of the island.

Whale sharks are filter feeders and take no interest in swimmers. The risks are the ordinary ones of open water: depth, boat traffic and fatigue. You should be a confident swimmer, wear the buoyancy aid offered if you are unsure, and keep clear of the tail, which is powerful.

Mostly between four and nine metres long, with a median of about six metres in the main scientific study. They are juveniles, and most are male. Fully grown whale sharks elsewhere are considerably larger, but adults are rarely seen at coastal feeding sites like this one.

By light aircraft. The flight from Dar es Salaam takes about half an hour, and there are also flights from Zanzibar and, in season, from Nyerere National Park. Baggage is limited to soft bags, usually around 15 kg. We do not use the local boats from the mainland.

No. The sharks feed in Kilindoni Bay on the west side of the island, and researchers note that their core area lies outside the marine park boundary. The park covers Chole Bay and the southern and eastern reefs, where most of the island’s lodges and diving are.

Last updated 3 October 2026

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