**4.2 Water bodies and underground rivers**

There are two underground river systems on each side of the city of Tulum: the southern system: Sac Ox Belha and the northern system: Sac Actun (map 3). These underground water body systems are connected to the cenotes. These systems are very vulnerable to all kinds of contamination, by sanitation systems: most houses have no drainage, only septic tanks whose absorption wells can contaminate underground rivers. The partial plan of the State of Quintana Roo, (2010) locates urban growth on the southern system of underground rivers (see map 4). The karstic rock soil is characterized by its high permeability; therefore, the infiltration of contaminants is very likely (**Figures 4** and **5**).

#### **Figure 4.**

*Underground rivers: South system: Sac Ox Belha and North system: Sac Actun (Source: Urban Development Plan, 2006–2030).*

#### **Figure 5.**

*Growth area of the city of Tulum on the southern system of underground rivers (Source: from the Municipal Development Plan).*

The current urban center does not have drainage and the porosity of the soil means that all matter is filtered and reaches the underground body of water. Fecal matter has already been found in the caverns. Urban growth without sewage treatment plants would lead to environmental and health catastrophes.
