For his participation in the Second Bruges Triennial in 1971, Raveel places four painted swans in the Bruges canals. Raveel initially wants to create a poetic effect but attention soon shifts to the ecological aspect of the matter: the canals are heavily polluted and the city council has the Swans removed because they cause consternation among the public. Raveel counters this and twice returns his Swans to the water. Thanks to the awareness he creates, Bruges' inland waters are purified.