Research around micro-hydro power is focused on technical aspects with limited understanding of the social organisation and environmental implications. We examine the ways in which micro-hydro is engaged by people and organisations as a means of contributing to the UK's policy ambition for renewable energy. We bring to the fore the way in which expertise is used and contested. A web based review of micro-hydro schemes in the UK was undertaken and a detailed evaluation of two schemes in the North of England was conducted to determine how expertise and contestation figures in community schemes. Results demonstrate a rapid expansion of micro-hydro in the UK. Ownership/control is highly 'community based'. Until now research around micro-hydro has been dominated by technical approaches with schemes defined in terms of hardware. We propose a third dimension to Walker and Cass's (2007) classification of renewable energy developments: the environmental dimension. We suggest this dimension of micro-hydro is critical, both in terms of the extent to which resources can be realised but also the ways in which it might attract controversy, in particular around how expertise is used and valued. (C) 2014 Elsevier Ltd. All rights reserved.