The Lagoa das Sete Cidades part of a natural landscape of communitarian interest: it is the largest body of water in the region and one of the most important freshwater resources in the archipelago.

The lake is situated within the caldera of the Sete Cidades Massif, an ancient volcano built on various layers of ash, pyroclasts and trachyte and basaltic lavas.

These geomorphological structures allowed varying hydrochemical properties and produced many types of springs and water circulation networks (Coutinho et al., 1996).

[4] Lacking a domestic sewage system until recently, the community of Sete Cidades contributed to gradual pressures on the ecosystem, resulting in an overabundant development of rooted aquatic macrophytes and algae in the water bodies.

[5] The eutrophication of the Lagoa das Sete Cidades lakes, due to nutrient enrichment was enhanced by human agricultural[6] and domestic activities, began to be noticed in 1987 and led to the implementation of a monitoring program.

When temperature, light and nutrient availability are adequate to phytoplankton growth, surface waters may host algae or cyanobacteria blooms.

[8] In eutrophic waters, cyanobacteria often dominate the summer and early autumn phytoplankton, while during winter and spring they are replaced by diatoms.

The Plano de Ordenamento da Bacia Hidrográfica da Lagoa das Sete Cidades (POBHLSC) (English: Sete Cidades Watershed Land Management Plan)[10] was implemented to evaluate the conditions of the lake, establish methods of interdiction and monitorization of landuse initiatives.