What makes the Pasig River swimmable?

DENR Class C (recreational, secondary contact) requires BOD below 7 mg/L and dissolved oxygen above 5 mg/L. The worst-affected lower Pasig sits near 42 mg/L BOD in its Class D state, so reaching Class C demands sustained sewerage coverage and budget over decades.

Pasig River cleanup

What does it take to make a dead river swimmable?

The Pasig was declared biologically dead in the 1990s. Drag the year, sewerage coverage and budget — watch the water turn from grey to blue as BOD falls toward DENR Class C.

Year

2026

BOD

— mg/L

Dissolved O₂

— mg/L

Status

—

Cleanup levers

Year2026

Each year of sustained effort draws BOD down toward the target.

Sewerage coverage target15%

Metro Manila 2024: ~15%. Singapore reached 100% by 2010.

Annual budget₱2B/yr

More budget accelerates the yearly drawdown rate.

Distance to swimmable—

BOD —

Cost per km

—

25 km · this scenario

Effort to Class C

—

at current settings

How to use

Drag year, sewerage coverage target and annual budget. The river animation changes color; BOD and dissolved oxygen update toward the swimmable thresholds, and the gauge shows how far the river is from DENR Class C.

What "swimmable" means

DENR Class C (recreational, secondary contact): BOD < 7 mg/L, DO > 5 mg/L, fecal coliform < 200/100mL. Class B (swimming): BOD < 5, fecal < 100.

Pasig today: BOD ~40 mg/L, DO ~1.5 mg/L, fecal coliform ~50,000/100mL — Class D, worse than Class C. Officially dead since the 1990s except briefly after typhoons.

The 2018 Magsaysay model

In 2018 the Pasig River Rehabilitation Commission won the Ramon Magsaysay Award — Asia's "Nobel" — for resurrecting the upper river. The model: estero-by-estero cleanup, relocating informal settlers off the banks, easements, and tributary interception, funded steadily over years rather than in one burst.

The lesson the sliders encode: progress is a function of sustained coverage × budget × time, not a single heroic project.

About the BOD baseline

The 42 mg/L starting BOD in this sim represents the worst-affected lower-Pasig reaches in their polluted Class D state (1990s–2000s peak readings of 40-50 mg/L per DENR-EMB). Recent PRRC monitoring (2018-2023) shows considerable improvement in upper Pasig (BOD 5-12 mg/L, Class C borderline) following PSSMP rollout, but tributaries (San Juan, Marikina, Manggahan) and the lower estuarine segment near Manila Bay remain elevated. The model therefore treats "the river" as a single worst-case segment for legibility; actual data spans an order of magnitude depending on location and season.

The model (Streeter-Phelps)

BOD falls from its 42 mg/L worst-case baseline toward a target set by sewerage coverage; budget controls how fast it gets there each year. As organic load (BOD) drops, the river's oxygen sag reverses and dissolved oxygen recovers — the core insight of the 1925 Streeter-Phelps BOD/DO model. Class C is reached when BOD crosses below 7 mg/L.

Citations

DENR-EMB Water Quality Monitoring (1996-2023) — Pasig River BOD & DO time series; Class D classification.
DAO 2016-08 — DENR Water Quality Guidelines & General Effluent Standards.
PRRC / DENR (2023) — Pasig River Rehabilitation Commission status report.
Streeter & Phelps (1925) — original BOD/DO sag model, U.S. Public Health Bulletin.
Lee & Tan (2008) — Singapore River cleanup history, Water Practice & Tech. 3.

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