This study takes a production function approach to examine the effects of farm wetland area for a set of producers in the Limousin region of France. By combining data from a recent survey of regional wetland areas with detailed farm-level production panel data, we find that maintaining wetland areas poses significant costs to farmers, in terms of foregone production value. These results help to explain the relatively low participation rate in agri-environmental schemes targeted to wetlands by farmers in this region. This represents a new application of the production function approach to estimate the cost of maintaining wetlands on working agricultural land, and is one of few studies to examine agricultural wetland costs outside of the US. This framework could be used to further inform payment incentives for agri-environmental schemes more generally.