Influenced by a visit to the Soviet Union, Tanzania's first president, Julius Nyere, imposed Swahili as the national language and relocated 120 ethnic groups to collective villages, utopias intended to eliminate tribal differences and provide education, medical care, and equal resources to all. (Critics contend that Nyere merely created an equality of poverty.) The Batongwe had lived on Lake Tanganyika's shore and in the Mahale Mountains since the fourteenth century, and the last holdouts were relocated, sometimes at gunpoint and with just four hours' notice, when the park was proclaimed in 1980. "This was good in the end, because Tanzania doesn't have the tribalism Kenya is suffering," Kabeth tells me. (My trip in January coincided with the eruption of violence between Kenya's Kikuyu and Luo peoples.) But he is full of nostalgia for his lost heritage, and on the long walk back shows us overgrown guava, lemon, mango, and raffia palm orchards, moss-covered clay pots, and other village remnants.

While the emphasis is on chimps, Greystoke Mahale also offers bird-watching, kayaking, snorkeling, and lazy afternoons out on the dhow. With the water mirror-calm, we vote to go fishing. The lake is home to gargantuan Nile perch and colorful kuhaye. Within minutes of leaving shore, Helen, Keith, and I begin reeling in two-pound kuhaye with turquoise-spotted cheeks, yellow backs, and black-spotted silver bellies. Kabeth has brought along soy sauce and a tube of wasabi and serves up white-fleshed kuhaye sashimi with wild ginger collected from the forest.

Our destination is a rocky cove a few hundred yards past the mouth of the Lubulungu River, where a lone hippo pokes his ears, eyes, and nostrils above the water. After the dhow circles to scare off crocodiles, hippos, and water cobras, we put on masks and float in shallow water. I see fish with whiskers, black-and-white checks, iridescent-blue and -green spots, and yellow stripes; fish shaped like torpedoes, inverted triangles, and even circles; and I see mouth breeders—fish that carry fertilized eggs and hatchlings in their mouths—and cuckoo catfish, who spit their own eggs into the mouths of mouth breeders, whose brood becomes food for the invaders' spawn. As the dhow motors away from this natural aquarium, Helen catches sight of two black forms approaching the shore to drink. "Wild chimps," Kabeth says in wonder, for we are far from the habituated M-group's territory. "We are very lucky to see them."

I had planned to travel south to Lupita by boat. But word comes by radio that the resort's Winsor Rose, Lake Tanganyika's first luxury yacht, is out of commission, its engine batteries drained by a twenty-three-hour voyage through nine-foot swells. (The convergence of the heat and humidity of the Congo Basin and the cool air of the East African highlands can give rise to sudden squalls.) When I finally reach the island by small plane and motor launch, the skies have cleared. But half-swamped wooden passenger boats and tiny overturned canoes testify to the lake's unpredictable moods.