In response to this competition for local resources, floodplain communities of the Middle Amazon are developing and implementing new forms of management of fish resources, based on traditional knowledge and collective agreements, with the aim of preserving the productivity of their fisheries. Local people claim the ownership of lakes near their communities based on the same notions of territoriality employed by other traditional populations for hunting and extractive activities. However, Brazilian legislation determines that all water resources and their fauna are public domain and does not guarantee regulation of access to these ‘common goods’. In this context, in the early nineties various initiatives for resolving the problem have been proposed for the region. The basic idea of the necessity to construct a locally negotiated and locally based consensus on access to natural, mainly aquatic resources, has been developed by the different projects according to specific local conditions. As part of this effort, the fishery department of the Brazilian Institute of Environment and Renewable Natural Resources-IBAMA implemented Project IARA. One major objective of this project was to create a data base to give scientific support to the adoption of efficient management measures. After collecting landing data for the Santarém market and length-frequency data for the most important fish species it was possible to apply some single-species stock assessment methods to assess the status and main features of the fisheries. These approaches permit us to conclude that large species with a high market value are being exploited intensively, and in some cases are already overexploited. On the other hand, smaller, opportunistic species seem to be more affected by environmental factors than by fishing effort. Simultaneously, research has been conducted by social scientists to investigate traditional management measures, aiming to understand the holistic approach taken by fishers. With regards to the community-based management one relevant question is how to evaluate the success of the measures. A comparison of fishing productivity in two lakes near the city of Santarém, one with a community-based management regime and the other without, demonstrated that the managed lake was approximately twice as productive as the unmanaged lake. Nevertheless, community based management also has problems, and frequently causes new conflicts both between community members and between the community and outsiders