There isn’t really a longer path along man-made Lake Paranoá. There are some nice parks with waterfront paths on both the northern end southern sides. Here are some favorite options for running:
Parque Deck Sul. Nice lakefront park in the Asa Sul residential district with views of the water and Ponte das Garças. A loop is ~1.5 km on cycle paths and a boardwalk path. Can be combined with nearby Parque Asa Sul. See our Asa Sul route.
Pontão do Lago Sul and Parque Ecológico Península Sul. 10.7 km out and back, 66m gain. Combine three parks just over the Ponte Presidente Costa e Silva bridge (JK Bridge). Paths in Praia Do Cerrado, the palm-lined paths of Pontão do Lago Sul, and the waterfront multi-use paths in Parque Ecológico Península Sul. The Parque Ecológico is the most extensive, with a paved ~3 km path along the water. We’ve mapped a nearly 11 km out and back, with a not so great road connection between the Pontão do Lago and Parque Ecológico.
Parque Vivencial II do Lago Norte. 3.5 km out and back, 21m gain. On the north side of the river, this attractive waterfront park has a nice gravel path along the water, making for a 3.5 km out and back.