Lagoa das Sete Cidade which stands for the Seven Cities Lagoon, is a small lake in the Portuguese archipelago of the Azores. It consists of two small lakes connected by a narrow passage (crossed by a bridge). It is located inside a dormant volcano cone in the east side of the island of São Miguel Island. It is the largest fresh-water lake in the Azores.
It is normally covered with clouds that fill the inside of the cone. In the few days that is uncovered, each side of the lake reflects the sunlight in different colors. This effect translates to the local names given to the small lagoons – one is known as the Green Lagoon and the other is known as the Blue Lagoon (Lagoa Verde e Lagoa Azul in Portuguese).
Due to the use of fertilizer in its shores the lake’s fauna and flora are environmentally threatened.