The city of Toowoomba, in south-eastern Queensland, is built on swamps. The swamps have been central to its history. From the mid-nineteenth century European colonists sought to control and contain them as a source of disease and damaging floods, while also being reliant on their aquifers for water supply. This paper considers the swamps as historical actors, paying particular attention to their ‘leakiness’ and ability to ‘trouble’ borders, boundaries and townships, a characteristic revealed within and against ongoing attempts to contain and control them. It focuses on the period from early British colonial settlement in the 1850s to the 1940s, in which the Council undertook significant and ongoing drainage works along with a range of other actions to ‘improve’ and civilise the swamps. The swamps instead ‘leaked’ out, with a kind of a spatial and temporal promiscuity. They moved underground though aquifers and through the air via miasma and mosquitoes, beneath and out into residential and commercial areas. They could reappear as floodwater, inundating homes and businesses. Used as grazing land, dumping grounds, and for market gardens, the swamps were ‘fluid’ actors that defied the colonial Council’s attempts at controlling and ‘civilising’ both people and ‘nature’.