Desafio do Cassó — Maranhão (Ultramaratona 2ª tappa)

In 1840, the town of Primeira Cruz functioned as a strategic garrison for Imperial forces during the Balaiada, a fierce social revolt that destabilized the province of Maranhão for three years. The soldiers stationed here monitored the movement of rebels across the fluvial-marine plains, relying on the complex network of river arteries that define the landscape to this day. While the military outposts have long since vanished, the water remains the primary connector of this territory, hosting the annual Desafio do Cassó on September 25th.

The conditions of Lake Cassó

The competition takes place in the Lagoa do Cassó, a sprawling natural pool that has served as a local fishery since at least 1870. Unlike the turbulent currents of the nearby Periá River estuary, which marks the boundary between Primeira Cruz and Humberto de Campos through a dense maze of mangroves and tidal flats, the lake offers calm, still waters. This stillness is a result of the unique geological formation of the region, where impermeable rock layers trap freshwater, a process similar to the one that feeds the seasonal lagoons found within the Lençóis Maranhenses. Swimmers navigating the 5000m, 1500m, or 400m distances will pass through a landscape protected since 1992 as part of the Upaon-Açu/Miritiba/Alto Preguiças Environmental Protection Area.

Race logistics and context

Organized by the Confederação Brasileira de Desportos Aquáticos, the event requires athletes to manage their effort in a freshwater environment that stays relatively uniform in temperature. The history of the area extends beneath the surface and into the subsoil; oil prospectors from Petrobras operated near the village of Caeté during the 1960s and 1980s, even drawing a visit from President Humberto de Alencar Castelo Branco after striking the São João I and II wells. Today, however, the only activity in these waters is the rhythmic stroke of competitors tracing the edges of the preserved lagoon.