Best TV-related April Fool's pranks?

There are a couple of famous April Fool's Day pranks from British TV history. Panorama (the British equivalent of 60 Minutes) did a report on April Fool's Day 1958 into a 'spaghetti harvest' taking place in Switzerland with fake footage of spaghetti being raked from trees and a voiceover from a trusted BBC news presenter. In 1977, there was a bogus science documentary called Alternative 3 which claimed the earth was about to suffer a major catastrophe and revealed that nations of the world had founded a survivor colony on Mars for their best and brightest. Unfortunately, the transmission date had to be changed and it just freaked people out when broadcast later in April!