An enduring challenge for environmental governance is how to coordinate multiple actors to achieve more collaborative and holistic management of complex socio-ecological systems. Catchment partnerships are often thought able to achieve this, so here we ask: do such partnerships actually help navigate complexity, or merely add to it? We answer this question by analysing the experiences of four voluntary UK catchment partnerships. Our data combined a structured desk-based analysis of partnership documents, with semi-structured interviews with partnership coordinators, chairs and partner representatives. These data were analysed using a qualitative thematic approach informed by the literatures on catchment management and collaborative governance of complexity. We found that partnerships both add to and help navigate the complexity of holistic and inclusive environmental management. Maintaining partnerships entails costs for partners, and partnerships connect messily and multitudinously to other initiatives. However, the partnerships were all judged as worthwhile, and made progress towards goals for water quality, biodiversity and river restoration. They were especially valued for envisioning and initiating complex activities such as Natural Flood Management. Communication and networking by partnership coordinators and partners underpinned these achievements. Aspects of pre-existing governance systems both enabled and constrained the partnerships: in particular, statutory agencies responsible for policy delivery were always important partners, and delivering partnership plans often depended on public-sector grants. This draws attention to the pervasive effect of governmentality in collaborative governance. More attention to analysing—and supporting—such partnerships is worthwhile, complemented by reflection on the limits to environmental governance in the face of complexity.