“The area around Rodrigo de Freitas Lagoon was initially inhabited by the Tamoio indians, who called it one of three names: Praguá (which means “fish cove”), Sacopenapã (“road of herons”) and Capôpenypau (“lagoon of shallow roots”). With the arrival of the Portuguese colonizers, the governor and Captain-General of the Rio de Janeiro Captaincy, António Salema, intended to install a sugarcane mill on the edges of the lake. To free it of the unwanted presence of the indians, he had clothes previously used by people with smallpox spread around the lake’s edges, resulting in the indians wearing them and subsequently dying. Thus began the sugarcane planting and the setting up of the d’El-Rey Mill, where today one finds the Visitor’s Center of the Rio de Janeiro Botanical Garden.
Later, these lands were acquired by the alderman Amorim Soares, with the lake being referred to as the “Lagoa de Amorim Soares”. With his expulsion from the city in 1609, the lands were sold to his son-in-law, Sebastião Fagundes Varela, with the consequent name-changing to “Lagoa do Fagundes”. This landowner, by acquisition and invasion, expanded his ownership of the region, and by 1620, he was already the owner of all the land that goes from modern-day Humaitá to Leblon.
In 1702, his great-grandaughter, Petronilha Fagundes, then 35 years old, married the young Portuguese calvary officer, Rodrigo de Freitas de Carvalho, then just 18 years old, and who would give his name to the lake. Widowed, Rodrigo de Freitas returned to Portugal in 1717, where he died in 1748…
Fonte da Saudade
The Fonte da Saudade, near the Praia de Piaçava . Towards the end of the 19th century and the start of the 20th, Portuguese laundry women who worked for rich families in Botafogo would get together around the fountain, washing clothes and sharing stories of missing their homeland.
The region stayed in the hands of the tenants without great fanfare until the beginning of the 19th century. Then, in 1808, the Portuguese Royal Family arrived during the transfer of the Portuguese court to Brazil. The Prince Regent appropriated the Engenho da Lagoa (Lagoon Mill) to build a powder factory and construct the Real Horto Botânico (Royal Botanical Garden)—today’s Rio de Janeiro Botanical Garden.
During the 19th century many diverse solutions were thought of for the problem of stagnated water—until, in 1922, the Bureau of Rural Sanitation presented a project to “…clean up and beautify the Capital for the Independence Centennial festivities.” That project involved dredging a canal to reconnect the lagoon to the sea, and deepen the land bar. The soil removed to build the canal formed the island of Caiçara, seat of today’s club of the same name.
In a short time, embankments formed on its edges, which gradually reduced its surface area, providing land for the Jockey Club Brasileiro, the Jardim de Alá, and the sport seat of the Clube Naval on the island of Piraquê. The dredged channel is now called the Jardim de Alá Channel.” [Wiki]
At the start of the 1970s, the most agressive form of real estate speculation ocurred in the area, which was invaded by construction companies that started landfilling the Lagoa even without government authorization, in order to build residential buildings. The Lagoa had already been enduring landfills since 1808 and had lost almost half of its original size. Many residents and arquitects protested, including Oscar Niemeyer and Lúcio Costa, demanding that the Lagoa be declared historic heritage.
This only came to happen in 1975 during the Marcos Tamoyo administration, who also approved a decree for the alignment of its edges. It was forbidden to alter the outline of the reflection pool. 
The Last of its Kind
The Rodrigo de Freitas Lagoon is the last lagoon within Rio’s city limits. The others – Desterro (Rua dos Arcos), Santo Antônio (Largo do Carioca), Boqueirão (in front of Lapa Aqueduct), Lampadosa (Praça Tiradentes) and Sentinela (near Catumbi) – were, at one time or another, landfilled to create new urban spaces. Being the only one left, and taking into consideration its history and the historical what-ifs below, one can imagine it might have looked quite different today.
1 – In the 1920s, for a short time, residents protested for the complete landfilling of the Lagoa. 2 – If the lagoon wasn’t partially landfilled over the centuries, it would be between one-third to one-half larger. 3 – Several favelas that have since been wiped from existence could have surrounded the lagoon. 4 – A maritime complex called Lagocean (#7) could have transformed the area between the lagoon and the sea.