The El Niño rains that fell during 1997-98 flooded Tanzania's Lake Manyara with fresh water.  Flamingos and other animals suffered more from "dilution" than "pollution."  Millions of flamingos were forced to fly away, having lost the blue-green algae that can grow only in water with a high concentration of mineral salts.   When the water became too diluted to support them, they left in search of a more alkaline environment.

Hippos Forced to Relocate
The rains also affected the Hippo Pools that clustered at the edge of Lake Manyara, the long, scenic lake that stretches between Tarangire National Park and Ngorongoro Crater.  These pools had hosted a wide variety of bird species as well as hippos, but during the rains, the pools merged with the lake as a whole.  The hippos have disappeared, and some people speculate that they may have journeyed to Ngorongoro Crater, which has several well-populated hippo pools.

Effects of El Niño on the Wildebeest Migration
The El Niño rains affected land animals as well.  Flooding blocked a crucial segment of the wildebeest migration route that runs through northern Tanzania and southern Kenya.   Since 1998, the wildebeest have not consistently followed their usual 500-mile circuit, clockwise.  Because customary weather cycles have been disrupted, the 1.5 million wildebeest have had to detour from their established route to avoid droughts and floods, sometimes splitting their herd and reversing the direction of their march to find grass.

Flamingos and the Rift Valley Lakes
Lake Manyara is part of a system of four lakes in the Great Rift Valley that acts as a single habitat for the entire flamingo population of East Africa.  (The others are Lake Natron in Tanzania and lakes Bogoria and Nakuru in Kenya.)  When conditions change in one lake, the birds fly to the others.  By using the lakes in a kind of rotation,  greater and lesser flamingos have maintained a relatively constant population of about 4 million birds during the last 15 years.

An Unusual Weather System
The rains of 1997-98 were the heaviest to fall on Tanzania since the big rains of 1982-83.    Both downpours were of the "El Niño" variety, named after the Christ child by Peruvian fishermen in the 1800s because the rains originate off the coast of Peru around Christmas time.

An El Niño is an exaggeration of a cyclic weather pattern.  Warm water flows south and accumulates in the South Pacific, just west of Peru.  This displaces north-flowing cold currents and causes dramatic changes in equatorial weather systems.  In 1997-98, El Niño was blamed for a host of phenomena besides the flooding of Lake Manyara, including fires in Indonesia, a reduction in violent storms in the Atlantic Ocean, intense blizzards in Colorado, an increase in the price of ice cream throughout the United States, and all manner of personal excuses.

There was a silver lining to the storm clouds over Tanzania:  by special arrangement, visitors can now explore Lake Manyara in a canoe.