Lagoa da Jansen is an urban lagoon located in the Ponta D'areia neighborhood of São Luís, the capital of Maranhão. The lagoon covers approximately 0.4 square miles and sits within a public ecological park that is open from early morning until late at night and free to access.

For paddlers and boaters, there is one documented access point and one boat ramp at Marina Aven - Associação De Vela E Transporte Marítimo Do Maranhão. The surrounding park includes a boardwalk running along the lagoon's edge, along with bike paths, sports courts, and restaurants, making the area well-developed for recreational use.

Water quality is a significant concern. Visitors consistently report persistent sewage odors and contaminated water, with the lagoon heavily polluted. Anyone considering paddling here should treat contact with the water as a serious health risk and take appropriate precautions. This is arguably the most important factor for paddlers to weigh when planning a visit.

The lagoon is situated in a fully urban environment, surrounded by city infrastructure and recreational facilities rather than natural shoreline. The setting offers views of the surrounding neighborhood and access to the broader amenities of São Luís, including proximity to Ponta D'areia beach and the historic center of the city. The park draws consistent local foot traffic, particularly in the evenings and on weekends, so the water surface may see activity from various users. Weekday mornings are the quietest time in the park overall.