In 1997, a river channel position shift, the so-called Masisea cutoff, occurred at the Ucayali River in Peru. A 71 km meander loop was cut-off and created a 33-47 km2 large oxbow lake. Besides flood events, especially those in 1997 when the cutoff occurred, the shift was mainly driven by human actions from the late 1980s onward. Residents from nearby upstream villages removed debris and cut vegetation along a small flood channel across the meander neck (where the cutoff took place) in order to improve transit and to establish a toll system. From the 1900s the channel and its connection to a floodplain lake have been used as a shortcut for canoes. A third reason for the cut off of vegetation was to facilitate bank erosion. Later, the channel was systematically maintained and widened with machetes, axes and shovels. Shallow, circular pits were excavated that acted as scour holes and in 1997 even a tractor was used to widen the entrance to the channel. The Masisea cut-off had significant impacts on the ecology and the economy upstream and downstream of the location at which it occurred. Upstream impacts consisted of a decrease in flood events, flood levels, travel time and transportation costs, which led to new economic opportunities such as changes in subsistence crops (e.g. plantain and maize) and cash crops that generated a higher income for people living upstream (e.g. papaya). In addition, the new economic opportunities upstream supported in-migration. However, downstream impacts consisted of an increase in flood events, flood levels, riverbed aggradation, bank erosion, lateral channel shifts and stranded communities. These impacts in turn led to a heightened vulnerability in floodplain agriculture, so that people increased their reliance on fishing and shifted their land-use from perennial to annual crops. Furthermore, the negative impacts led to upstream migration.