Açude Engenheiro Ávidos, also widely known as Boqueirão de Piranhas, is a large reservoir located in the district of Engenheiro Ávidos, in the rural zone of Cajazeiras, in the Alto Sertão region of Paraíba, Brazil. The city of Cajazeiras lies approximately 468 kilometers from the state capital, João Pessoa. The reservoir was formed by damming the Rio Piranhas, and with a storage capacity of approximately 293,617,376 cubic meters, it ranks among the largest reservoirs in Paraíba.

Construction of the dam began in 1921 and was completed in 1936, carried out by the federal agency then known as IFOCS, today the DNOCS (Departamento Nacional de Obras Contra as Secas). The reservoir was named in honor of engineer Moacyr Ávidos, who was associated with the project. It sits at a municipal boundary, with drone imagery showing the broad expanse of open water set against the caatinga landscape typical of the semi-arid sertão paraibano.

The reservoir serves multiple functions: water supply for Cajazeiras and surrounding municipalities, irrigation, and fishing. It also plays a role in the Transposição do Rio São Francisco (the São Francisco River Transposition project), receiving supplemental water through the northern axis of that infrastructure, which helps maintain storage levels and supports redistribution of water to cities in both Paraíba and Rio Grande do Norte.

The surrounding landscape is characteristic of the northeastern Brazilian caatinga — arid, semi-arid terrain with sparse, drought-adapted vegetation. The reservoir's size and open character mean paddlers can expect exposure to wind and sun, conditions common in the sertão. The region experiences a semi-arid climate with pronounced dry and wet seasons, which will influence water levels and surface conditions throughout the year.

Paddlers should contact local authorities or DNOCS directly to confirm current access arrangements and any applicable regulations before launching.