The control of agricultural nonpoint source pollution is emerging as a priority of state and national pollution control programs. Best management practices (BMPs) are often proposed as a method of control. Many BMPs are perceived by farmers as having economic disadvantages when compared to conventional management systems. In the absence of tougher environmental restrictions on farmer behavior and complete observability of individual farmer actions, it may be necessary to provide economic incentives to encourage farmer adoption of BMPs within environmentally sensitive watersheds. This study investigates the use of a group incentive contract to encourage adoption of BMPs. The idea behind the group incentive contract is to compensate farmers for actual damages due to adoption of BMPs while avoiding moral hazard problems and exploiting the correlated risks that farmers in a watershed face. Simulation results indicate that the majority of the nitrate pollution generated by central Illinois corn growers could eliminated at little or no cost.