Farmer-managed irrigation systems (FMIS) in the high altitude valleys of the Karakorum, Pakistan, continue to be managed effectively despite increased pressure on the social arrangements that sustain them. Colonial era records shows that over a century ago government agencies undertook irrigation support projects. In the past three decades, government agencies and the non-government agency Aga Khan Rural Support Programme (AKRSP), which channels foreign funds into the region, have actively engaged in the provision of irrigation support. This article seeks to explore whether such projects support or undermine farmer-managed irrigation systems and the complex institutional arrangements that underpin them. Field research using ethnographic and participatory methods was conducted in spring 2013 in the upper Shigar valley, Skardu district, Gilgit-Baltistan. The findings show that irrigation development is a political activity that involves village-based actors, religious leaders, local politicians, and government and non-government agencies. Government agencies operate in a largely top-down, engineering mode, their larger projects limited to villages suffering water scarcity. The local government provides small funds for renovation work of FMIS, though allocation of funds is highly politicized. Non-government agencies, for a variety of reasons including donor-funding cycles, apply a one-size-fits-all ‘participatory’ model in an attempt to socially engineer rules and institutions. In communities divided by factionalism the use of such external models that stress formation of committees are unlikely to yield positive results, and could instead contribute to undermining the very systems they seek to support. This research argues that irrigation interventions should take care to build upon the rich and complex social arrangements that have sustained FMIS through the centuries.