The duck _____.

Loch Ness has long been famous for its monster but in 1978 a visitor to this Scottish lake could have seen something quite different - a duck. This wasn't an ordinary duck. It had no feathers and it could not fly. In fact, it was made of metal and had been placed on the lake for a purpose. The purpose was to test the cost of using water energy to produce electricity. The duck was one of many all of which were connected. As the water was moved by the wind, the ducks moved up and down, and this movement was used to produce electricity.