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Paean to a Dying River: Measuring Water Quality of the Beleaguered Pasig River in Metro Manila, Philippines

The Pasig River, one of the major Philippine river systems, connects Laguna de Bay to Manila Bay. Spanning 25.2 kilometers (15.7 miles), it bisects the Philippine capital of Manila and its surrounding urban area into northern and southern halves. Its major tributaries are the Marikina River and San Juan River. The total drainage basin of Pasig River, including the basin of Laguna de Bay, covers 4,678 square kilometers (1,806 square miles).

The Pasig River figured as an important transport route and source of water for Manila during the Spanish era. Unfortunately, as a result of negligence and industrial development, the river evolved into a highly polluted water body. In fact, it is considered by many ecologists as biologically dead or is unable to sustain life.

The Pasig River Rehabilitation Commission (PRRC), a state entity under the Office of the President, was tasked with rehabilitating the Pasig River. The commission served for 20 years, from 1999 until its dissolution by President Rodrigo Duterte in November 2019. The commission’s powers and functions were transferred to the Manila Bay Task Force and the Department of Environment and Natural Resources (DENR).

This report presents quantitative water quality data in the Pasig River tributary communities (esteros) of Maypajo, Sunog Apog, Vitas, San Lazaro, Kabulusan, Magdalena, Binondo, and De la Reina all situated within the Metro-Manila area. Scientific data came from the PRRC’s Environmental Division that performed on-site, laboratory, and sedimentary analyses.

According to the California State Water Resources Board, the “vital signs” or  the five basic water quality parameters that are basic to life within aquatic systems are dissolved oxygen (DO), temperature, electrical conductivity/salinity, pH, and turbidity.  Impairments of these can be observed as impacts to flora and fauna in a given water body. Additional water quality parameters such as biochemical oxygen demand (BOD), total coliform and total fecal coliform will also be discussed.

Dissolved oxygen (DO) refers to the amount of oxygen dissolved in water.  Because fish and other aquatic organisms cannot survive without oxygen, DO is the most important water quality parameter.  DO is usually expressed as a concentration of oxygen in a volume of water, i.e. in milligrams of oxygen per liter of water or mg/L.

The DENR standard for DO is greater than or equal to 5 mg/L.  Aquatic life is put under stress when DO concentration falls below 5.0 mg/L. Good fishing waters have a DO of at least 9.0 mg/L.  Conversely, fish kills may result in waters with DO less than 2.0 mg/L.

DO can also be expressed as percent saturation or the amount of oxygen in a liter of water relative to the total amount of oxygen that water can hold at a certain temperature.  The DENR minimum percent saturation standard is 60%.

Against these DENR standards, all eight esteros showed very low DO concentrations, failing to meet the 5.0 mg/L benchmark.

All 8 esteros likewise  failed to satisfy the DENR standard of at least 60% saturation with their very low saturation levels ranging from a low of 7.58% in Binondo to a high of merely 38.04% in Maypajo.

Temperature is a measure of the average kinetic energy of water molecules.  It is measured on a linear scale of degrees Celsius/Centigrade or degrees Fahrenheit.

It is one of the most important water quality indicators because it influences DO concentration, photosynthetic rates of algae and other aquatic plants, the metabolic rates of organisms and their sensitivity to toxic wastes, parasites and diseases.  It also affects the timing of reproduction, migration, and estivation of aquatic organisms.

The optimal health of aquatic organisms, from microbes to fish, depends on temperature.  If temperatures are outside the optimal range for a prolonged period, organisms are stressed and may die.

Temperature not more than 20 degrees Celsius or 68 degrees Fahrenheit does not create a climate for fish diseases.  If the temperature is often more than 13 degrees Celsius or 55 degrees Fahrenheit, this creates a climate right for many fish species plants, insects, nymphs, and some fish diseases.  Temperatures below 13 degrees Celsius reduces plant life as well as indicate uninhabitable water for salmon.

The DENR standard for Class C waters (used for propagation of fish and other aquatic resources, boating, fishing, agriculture, irrigation and livestock watering) is an allowable temperature increase over the average ambient temperature for each month or a maximum rise of 3 degrees Celsius.

All eight esteros far exceeded 3 degrees Celsius and hence failed to meet the prescribed DENR standard.  The highest excess in temperature was noted in Sunog Apog (28.7 degrees Celsius), while the lowest was seen in Maypajo (26.45 degrees).

Electrical conductivity is the ability of water to conduct an electrical current.  It is expressed in micromho (U.S. preferred term) or microSiemen (European preferred term).  One micromho is equal to 1 microSiemen.

This measure is an indication of the quantity of dissolved solids (inorganic acids, bases, and salts) in the water.  The electrical conductivity of water is directly related to the concentration of these dissolved solids.  Ions from the dissolved solids in water influence the ability of that water to conduct an electrical current as measured by a conductivity meter.

The more ions that are present, the higher the conductivity.  Distilled or de-ionized water can act as an insulator due to its negligible conductivity value.  Conversely, seawater has a very high conductivity.

Significant changes in conductivity, whether due to natural flooding, evaporation or man-made pollution can be very detrimental to water quality.

There is no DENR standard for conductivity.  However, the U.S. standard for drinking water set by the Environmental Protection Agency’s (EPA) National Secondary water standards is less than or equal to 900 microSiemens/micromhos per centimeter.

In most rivers and lakes with outflows, conductivity ranges between 10 and 1,000 microSiemens/centimeter.  In American freshwater streams, the average conductivity ranges from 100 to 2,000 microSiemens per centimeter.

Viewed against the EPA criterion, all eight esteros met the benchmark with their low conductivity values ranging from a low of 0.77 in De la Reina to a high of 24.39 in Sunog Apog.

Salinity is an estimate of the level of salt in a water sample.  It is derived from a conductivity reading using a 0.5 conversion factor.  It is expressed in parts per thousand (ppt) or grams per kilogram.

The average river salinity is 0.5 ppt while the average ocean salinity is 35 ppt.  Moreover, the following are approximate values of salinity in ppt based on source:  freshwater (less than or equal to 0.5);  brackish/estuary (0.5-17);  black sea (16);  ocean range (32-37);  ocean average (35).

Based on these average values, the waters of Sunog Apog with a salinity of 2.44 ppt  falls in the brackish/estuary category. The waters of Maypajo, Kabulusan, Magdalena with salinity values less than 0.5 ppt belong to the freshwater category.

Salinity is an important water quality parameter because it affects DO solubility.  The higher the salinity, the lower the DO concentration.

Moreover, salinity is important because it poses a major threat to freshwater systems. Organisms thriving in these systems can only tolerate a specific range of salinity.  Salinity values outside the normal range can result in fish kills due to changes in DO concentration, osmosis regulation, and total dissolved solids (TDS) toxicity.

 pH is a measure of how acidic or basic (alkaline) a water source is.  The pH scale is logarithmic and goes from 0 to 14.  For each whole-number increase (e.g. from 1 to 2), the hydrogen ion concentration decreases ten-fold and the water becomes less acidic.  As pH decreases, the water becomes more acidic.  As pH increases, water becomes more basic or more alkaline.

pH values less than 7 are acidic, while pH values exceeding 7 are basic or alkaline.  A value of 7 is neutral. pH values less than 4.8 or greater than 9.2 can be harmful to aquatic life.

As water becomes more basic or alkaline, the pH increases many chemical reactions inside aquatic organisms (cellular metabolism) that are necessary for survival and growth.  Organisms require a narrow pH range. At the extreme ends of pH (2 or 13), physical damage to gills, exoskeleton, and fins occur.  Most valuable fish species such as brook trout are sensitive to changes in pH.  Immature stages of aquatic insects and immature fish are extremely sensitive to low pH values less than 5.0 and may die.

Changes in pH may alter the concentrations of substances in water to a more toxic form.  For example, a decrease in pH (below 6) may increase the amount of mercury soluble in water.  On the other hand, an increase in pH (above 8.5) enhances the conversion of non-toxic ammonia (ammonium ion) to a toxic form of ammonia (un-ionized ammonia).  Low pH levels (acidic water) also accelerate the leaching of heavy metals harmful to fish and other aquatic organisms.

The DENR pH standard for Class C waters establishes the optimum range of 6.5 to 8.5.  Only Binondo met such standard.  The other 7 esteros showed acidic levels with pH values lower than the prescribed lower limit of 6.5.  The most acidic waters came from Magdalena which had a pH of 6.05.

Turbidity is a measure of the amount of suspended particles in water.  It is also a measure of water clarity or transparency which indicates how far light can travel through water.  Suspended particles that reduce clarity may include organic particles (microbes, algae, plant particles, animal detritus) and inorganic particles (e.g. silt and clay), sewage, and industrial waste.

High turbidity may result from high amounts of suspended particles and the presence of dark-colored humic acids coming from decaying vegetation common in peat bog waters.  When turbidity is high, water loses its ability to support a diversity of aquatic organisms.

Oxygen levels decrease in turbid waters which become warmer due to the greater heat absorption from sunlight by the suspended particles.  The consequent decrease in light penetration as a result of high turbidity results in decreased photosynthetic activity which, in turn, decreases the amount of oxygen in the water.

High amounts of suspended solids (a mark of high turbidity) can clog fish gills, reduce growth rates of aquatic organisms, reduce disease resistance, and prevent or slow down egg/larval development.

Settled particles make river-bottom microhabitats unsuitable for mayfly nymphs, stonefly nymphs, caddis fly larvae, and other aquatic insects.  The sediment can also carry pathogens, pollutants, and nutrients which may result in fish kills.

There are no specific standards for turbidity.  However, Mitchell and Stapp (1986) suggested a guideline level of 23 NTUs.  Viewed against this standard, all 8 esteros have substantially higher values. Among the 8 esteros, the most turbid or murkiest water came from San Lazaro (158.94), while the least turbid was Sunog Apog (26.91).

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms (those requiring oxygen for their metabolism) in a body of water to break down organic material present in a given water sample.  Alternatively, it is defined as a measure of the oxygen utilized during organic matter degradation at a specific time and temperature.

High BOD levels indicate a condition where there is a reduction of oxygen availability to the microbial population to degrade organic content in a particular water sample.

The DENR standard for Class C waters is a BOD level equal to or less than 7.0 milligrams per liter.  This criterion suggests that lower BOD values are signs of good water quality.

Compared with the DENR standard, all 8 esteros’ relatively high values exceeded the 7.0 upper limit which imply low oxygen availability. The lowest BOD reading was observed in Sunog Apog (32 mg/L), while the highest was in San Lazaro (121.67).

Coliform is a very common rod-shaped bacterium. It is relatively harmless, not thought of as disease-causing to humans, and lives in large numbers in soils, plants, and intestines of warm-blooded (humans, mammals) and cold-blooded animals (snakes).  Coliform found in the gastrointestinal tract of humans aids in digestion of food.

Because pathogenic bacteria in wastes and polluted water are usually much lower in numbers and much harder to isolate and identify, the coliforms which are usually in high numbers in polluted waters are used to determine total coliform which is viewed as a general indicator of potential contamination of a water source with pathogenic and disease-causing organisms.

The DENR standard for Class C waters, is less than or equal to 5,000 MPN (Most Probable Number) per 100 milliliters of water.  All 8 esteros failed to meet this standard, as shown by counts way exceeding the prescribed maximum limit.

San Lazaro had the highest total coliform (13,300,000 MPN/100 ml. of water), hence the worst water quality.  Binondo showed the lowest count (2,160,000 MPN/100 ml. of water, thus the best water quality according to the total coliform criterion.

Fecal coliforms are the coliform bacteria that originate specifically from the intestinal tract of warm-blooded animals (e.g. humans, raccoons, beavers).  The fecal organisms themselves are not harmful but because they live in the same portion of the digestive system where disease-causing microorganisms occur, the presence of fecal bacteria in a water sample indicates that such sample might contain microorganisms harmful to human health.

Fecal coliform provides stronger evidence of fecal contamination than total coliform counts.  Fecal coliform could not be distinguished as human or animal.

  1. coli is the indicator organism of choice for fecal contamination. However, there is another group of fecal coliform, the thermotolerant fecal coliform which are differentiated from total fecal coliform using elevated temperatures (43 to 44.5 degrees Celsius) during incubation.

Very high levels of fecal bacteria can give water a cloudy appearance, cause unpleasant odor, and increased BOD.  Sources of fecal bacteria in surface waters include outflow from wastewater, domestic and animal manure, on-site septic tank overflow and discharge, outflow from wastewater treatment plants, storm runoff, and direct fecal discharge into water bodies.

Worldwide, there are varying standards for total fecal coliform.  The DENR standard for Class C waters is less than or equal to 200 MPN/100 ml. water.  The World Health Organization set 103-104 CFU (colony-forming units)/100 ml. water as the standard for water reused in aquaculture and agriculture.  For water used in recreation and industrial processes after treatment, the WHO specified 1,000 CFU/100 ml. water for total fecal coliform and 5,000 CFU/100 ml. water for total coliform.

All 8 esteros far exceeded above-mentioned total fecal coliform criteria. The highest total fecal count, hence the worst water quality, was seen in Maypajo (7,040,000 MPN/100 ml. water).  The lowest, thus relatively the best water quality, was in Binondo (4,800,000 MPN).

In conclusion, most of the numerical water quality indicators reveal a high level of pollution. All 8 esteros failed 3 of the 5 vital signs of water quality, namely, dissolved oxygen, temperature and turbidity.

Moreover, BOD level, total coliform and total fecal coliform counts far exceed benchmarks. These findings indicate an urgent need to immediately reduce the influx of human and industrial wastes into the Pasig River. To do this, residents of esteros must be encouraged to connect to sanitary sewage systems. Equally important is the strict implementation of laws prohibiting the discharge of industrial wastes into the river, a task easier said than done.

Freddie R. Obligacion ( is an alumnus of The Ohio State University-Columbus (MA, PhD sociology) and the University of the Philippines-Diliman (MBA Honors and BS Psych., magna cum laude). He is currently studying leadership preferences and the community impact of grassroots entrepreneurship.


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