The Great Lakes of East Africa rose abruptly in the early 1960s, when tremendously wet conditions occurred throughout the region. The high stands remained for a decade over longer in most lakes and were interpreted as a protracted wet period in East Africa. A hydrologic model of Lake Victoria was constructed and "inverted" to interpret lake levels in hydrologic terms, including regionally averaged rainfall. The so-determined regional rainfall series showed that the high stands were a result of only two or three wet years, but these created a new equilibrium stand of the lake. The wet years were linked to high SSTs in the Atlantic and Indian Oceans and a Pacific el Nino event. This appears to have been the case for the other great lakes as well, most notably Lake Tanganyika. Similar high stands suggested a protracted wet period towards the end of the 19th century. Application of the model showed that a rapid rise was associated with one of the strongest el Ninos on record c. 1877 or 1878. Again, one or two wet years produced a multi-decade high stand of the lakes. The high stands of the lakes dramatically changed the biogeochemical system of the lake, as shown by major changes in Lake Victoria in the 1960s.