This paper explores the ambiguous role of magic in the controversy over the draining of the fens, the last bastion of wilderness in seventeenth-century England. In what now looks like an early form of environmentalist resistance to the destruction of these wetlands, opponents of the drainage accused the undertakers of invoking diabolical aid in their audacious efforts to tamper with God’s creation. Evidence of this mentality can be found in both William Shakespeare’s The Tempest and Ben Jonson’s The Devil is an Ass. Via a close reading of Jonson’s comedy, this paper navigates the confluence of magic, technology, and “projection” in the ideological debate surrounding the fens. Just as the traditional Vice figures (Iniquity and Pug) find themselves out-devilled by Jacobean Londoners, the play dramatizes the appropriation and displacement of a residual poetics of enchantment by the emergent discourses of economics and applied engineering. A tendency to equate magic with hydro-engineering technology may have been encouraged by John Dee’s involvement in the project. Drawing on an unpublished manuscript in the Ashmole collection at the Bodleian Library, this paper seeks to uncover the extent and impact of Dee’s role in the drainage. Advocates of the drainage, however, not only denied any supernatural involvement but also counterattacked by accusing their opponents of credulity and magical thinking. They characterized the native fen-dwellers as superstitious heathens and cast a scathing eye on local folklore depicting the fens as a demon-haunted wasteland. In pro-drainage documents, the proposed draining of the fenlands becomes tantamount to an exorcism, purging the rural backwaters of paganism and witchcraft. Wetlands management will now be conducted through applied engineering rather than magical incantations. A little known Jacobean ballad, “The Powte’s Complaint” (c. 1619) revives these animistic tropes to protest the fen’s destruction. Jonson’s play may explain why this tactic was doomed to fail and why this poem has been forgotten. As the credibility of magic eroded in the mid-seventeenth century, opponents of the drainage instead sought to stir up public resentment against the foreignness of the Dutch under-takers rather than their supposed collusion with supernatural forces. Jonson’s own projection that the drainage was an impossible con (like alchemy) would prove inaccurate. Nevertheless, The Devil is an Ass stands as the one of the most ecologically-engaged texts in the canon of early modern English drama.