Figure 1
Map of the study meso-basins — Alto Tietê, Sorocaba/Médio Tietê, and Piracicaba-Capivari-Jundiaí (PCJ) — highlighting the main monitored rivers.
Table 1
Parameters, units, and scoring criteria used in Observando os Rios (WQI).
| PARAMETERS | UNITS | SCALES | |||
|---|---|---|---|---|---|
| Turbidity (Tb) | UTJ | Tb > 100 | 40 < Tb < 100 | Tb < 40 | Not verified/measured |
| Total Coliforms (TC) | TC | Positive | – | Negative | |
| Dissolved oxygen (DO) | mg L–1 | DO < 4 | 4 < DO < 6 | OD > 6 | |
| Biochemical oxygen demand (BOD) | mg L–1 | BOD > 8 | 4 < BOD < 8 | BOD < 4 | |
| Hydrogen potential (pH) | – | (pH < 5) or (pH > 9) | (7 < pH < 9) or (5 < pH < 6) | (6 < pH < 7) | |
| Nitrate (NO3) | ppm | NO3 > 20 | 5 < NO3 < 20 | NO3 < 5 | |
| Phosphate (PO4) | ppm | PO4 > 2 | 1 < PO4 < 2 | PO4 < 1 | |
| Settleable solids (Ss) | mm | S > 3 mm | S < 3 mm | None | |
| Floating trash (Ft) | – | Frequent | Few | None | |
| Smell (Sm) | – | Fetid | Weak | None | |
| Fish (Fh) | – | None | Few | Muitos | |
| Red Larvae and worms (R/lw) | – | Frequent | Few | Nenhum | |
| Transparent/dark worms (TD/lw) | – | None | Few | Frequent | |
| Foams (Fs) | – | Frequent | Few | None | |
| score | 1 | 2 | 3 | 0 | |
Figure 2
Water Quality Index (WQI) qualification scales – colorimetric and numerical – for Observando os Rios program (OoR) and the São Paulo State Environmental Agency (CETESB), and percentage representation of each qualitative category across the different methods.
Figure 3
Annual mean values of the Observando os Rios Water Quality Index (IQA_OoR; A), the CETESB Water Quality Index (E), and OoR-based conversions (OoR_CET; B, OoR_CET_8; C, and OoR_CET_8*; D) by mesobasin. Colors indicate classification categories based on the CETESB scale (0–100), except for column A, which uses the original OoR scale.
Figure 4
Agreement between Observando os Rios (OoR) and CETESB water-quality classifications across the three hydrographic mesobasins (Alto Tietê, Sorocaba/Médio Tietê, and Piracicaba–Capivari–Jundiaí). Bars indicate exact agreement, and the dashed line represents agreement within ±1 classification category.
Figure 5
Agreement between Observando os Rios (OoR) and CETESB water-quality classifications at co-monitored sites along the Tietê River (Alto Tietê mesobasin). Bars indicate exact agreement, and the dashed line represents agreement within ±1 classification category.
Figure 6
Annual sample completeness (number of parameters measured per sampling event, ranging from 11 to 14) and total number of sampling events in the Alto Tietê, Sorocaba/Médio Tietê, and Piracicaba–Capivari–Jundiaí mesobasins (2002–2023).
Figure 7
Comparison of the number of water-quality sampling events conducted in the study mesobasins by the Observando os Rios program (OoR) and by CETESB.
Figure 8
Annual sampling effort per municipality in each mesobasin (a–c). Highlighted colors indicate the most representative municipalities, while all others appear in light gray as “other municipalities.”