title: John Hanning Speke
context: They had also heard of a second lake to the north-east, and in May 1858, they decided to explore it on the way back to the coast. But Burton was too weak to make the trip and thus stayed in base camp when the main caravan halted again at Kazeh.[8] Speke went on a 47-day side trip that was 452 miles up and down in which he took 34 men with Bombay and Mabruki as his captains[8] and on 30 July 1858 became the first European to see Lake Victoria and the first to map it.[9] It was this lake that eventually proved to be the source of the River Nile. However, much of the expedition's survey equipment had been lost at this point and thus vital questions about the height and extent of the lake could not be answered easily. Speke's eyes were still bothering him and he only saw a small part of the southern end of the lake and his view was blocked by islands in the lake so he could not judge the size of the lake well. However, Speke did estimate the elevation of Lake Victoria at 4000 feet by observing the temperature at which water boiled at that level.[8] (This lake's being substantially higher than Lake Tanganyika did make it a more likely candidate for the source of the Nile.)
question: When was Lake Victoria found by John Hanning Speke?
answers.text: 30 July 1858 30 July 1858