Baseline Assessment of the Current Environmental Condition of the Naga River

Completed: 2013
Prepared by: Dr. Emelina G. Regis, Rochelle P. Reyes
Funding Agency: City Government of Naga

The Study of the Naga River was conducted because of the worsening sad state of the said river which has been impacted by waste accumulation, pollution of land and waterways that resulted to foul smell and flooding due to clogging of its drainage. In this study, the Institute for Environmental Conservation and Research (INECAR), of Ateneo de Naga University, was chosen to conduct the research project with the following objectives:

In general, the study intends to provide the LGU of Naga City with baseline information on the environmental conditions of the Naga River. Specifically, it aims to measure the following parameters: a) Physical and Chemical states of the river water and sediments; b) Biological components existing in the River and its riparian zone, especially indicator species; and c) Sources of pollutants.

The study started with hiring of research and field assistants who were given orientation through workshops. The preliminary activities of the assessment included reconnaissance survey to determine the nonpoint sources and point source and of pollution. This led to the establishment of 5 nonpoint source sampling stations and 1 point source sampling station using GPS. The mid-tide was also determined which is when the water was unmoving for about 2 hours. Other activities include purchase of materials, calibration of equipment, and cleaning of containers with acid-wash method. Then, standardization of the methodology was done on site (outside of Naga River), specifically at the Canaman segment of the Bicol River, as training to guarantee accuracy in the conduct of sampling in Naga River.

The materials analyzed were water and soil/sediments while the physico-chemical parameters observed and recorded were depth, color, odor, temperature, transparency, pH, turbidity, total
dissolved solids (TDS), conductivity, dissolved oxygen, pH, salinity, nitrate and phosphate, toxic heavy metal lead (Pb and mercury (Hg) using various equipment and instruments from the INECAR.

The biological components are plants and animals still surviving in Naga River. The land plants are those thriving in the riparian zone. One species of floating/semi-submerged plant – Eichhornia crassipes (local name: water hyacinth) is also listed. The fauna are the fishes, mollusks and crabs since these were the only animals found in the sampling sites.

The levels of Toxicity of the river is based on an indicator: Toxic Phytoplankton Count.

The findings

1. In terms of depths, there are some shallow portions (0.7 and 1.2 m) which can easily heat up during summer months especially at mid-day. The shallowest part of the river is Station 4 while the deepest portion is Station 1. However, the wide ranges in depth readings also show variability in depths of the entire river bottom.

2. The water temperatures recorded are higher and more variable in October, 2011 than in January 2012 which shows almost constant temperature.

3. The odor of the river water can be described as Obnoxious, Putrid, and Foul. Obnoxious is technically defined as strongly offensive and irritating to the nose; Putrid is rotten/in state of decay; and Foul is unpleasant odor but still tolerable to the nose. In terms of color, the water ranges from light brown to murky brown. However, there are areas that show light greenish brown in color yet murky in appearance. This condition indicates the presence of microscopic green algae that comprise of phytoplankton, both harmless and harmful. The color of soil/sediment is described as
brown to grayish black while its odor is predominantly earthy.

4. Due to the murky appearance of the river water, transparency is low from 17.5 to 40.5 cm only, whereas, the standard is 61 cm.

5. Although the values of TDS in this study are lower than the standards of DENR and Bauder and Sigler, in both sampling dates, Stations 1 and 2 were recorded to have the highest TDS (Table 7). This condition is due to the stations’location (near mouth of Naga River) which receives water from the Bicol River and contributes fresh water into the Naga River segments during high tide. Nevertheless, these levels did not exceed the maximum level of 500 ppm with the exception of Station 1 in October 2011 which recorded 621.9 ppm.

6. All the study Stations are within the standards for Conductivity which is below the maximum of 500 μhos/cm or micromhos per centimeter. However, low levels of Conductivity indicate high input of organic compounds that lower Conductivity.

7. In terms of Dissolved Oxygen (Miller, 2000), the water quality of Naga River in October 2011 ranges from Slightly Polluted (Station 5) to Gravely Polluted (Statio 3). In January 2012 sampling however, the water quality ranges only from slightly polluted (Stations 1 and 5) to moderately polluted (Stations 2 –4).

8. The recorded pH level of the Naga River in this study is within acceptable limit but with tendency towards alkaline condition. This condition may have resulted from different inputs that the river received from its sources in the upper reaches, the inputs from lower Naga, and from the Bicol River during high tide.

9. In terms of pH, values obtained did not exceed pH 7.3. Alkaline soil suggests the presence of calcium carbonates and possibly marine influence while Acidic soil indicates volcanic origin. For salinity, the amount of salt in the river water is below 1 part per thousand (ppt). The standards is 0.5 parts per thousand (ppt or 0.5 ‰). Also, the presence of salts within the values of 1 –5 indicates the presence and availability of nutrients for plant growth on soil.

10. With regards to Phophorus and nitrates, the former is responsible for the algal bloom and eutrophication of Naga River. The increased in the level of phosphorus in water bodies could be due to malfunctioning septic systems and its use as indispensable ingredient of fertilizer and detergents. Under eutrophic condition, dissolved oxygen (DO becomes low and results in death of fishes and invertebrates that thrive in water such as mollusks and fishes. In this study, nitrate did not exceed the standard of 10 mg/L in all the sampling events. The most likely reasons for the high phosphorus levels are: a) New Year celebration where firecrackers (basically phosphorus) have been lighted and residues contaminated the river, b) major cleaning activities by each household in Naga City and adjacent towns along the Bicol River heavily using detergents after the Christmas and New Year celebration, and c) planting season started in January when rainwater are still sufficient to support the needs of growing crop plants until the onset of summer and harvest time. Since phosphate is also an indispensable nutrient for plants, both terrestrial and aquatic, including phytoplankton, increases in phosphate even with low nitrate, could trigger eutrophication of water bodies such as the Naga River.

11. The level of contents of toxic metals such as lead (Pb) and mercury (Hg) are within the standards based on Kloke (1981). Similarly, as in the water samples, the heavy metals in sediments are also below the toxic levels. Nevertheless, the level of Lead in sediments at Station 3 has exceeded the natural content indicating external sources of contaminants in the sampling station which is Panganiban bridge to Colgante bridge.

12. The riparian vegetation of the Naga River consists of 67 species of plants excluding water hyacinth because this species is not on land but on water and mobile during the rainy season. Most likely the majority of these plants are planted and/or maintained by the building occupants for various uses (shade, medicine, ornamental, and/or food). Of these plants, 49.25% are trees; 10.45% are shrubs; 5.97% are weeds; 11.94% are ornamental and 22.39% are used as food.

13. In terms of level of fish abundance, there are more fishes near the mouth (Station 2) of Naga River than the other stations during October 2011 samplings with Station 3 recording 0 species/individuals.. There are also more fishes at the mouth (Station 1) during January 2012 samplings than the rest of the stations with Stations 2 and 5 recording the lowest.

14. The data presented in the results of toxic phytoplankton count is sad and problematic because all the sampling stations reached the highest level of toxicity which is III. This means that the river is dying in terms of toxicity because the kind of species indicates the presence of very harmful toxins produced by toxic phytoplankton.


Naga River is dying because of the following conditions of its ecosystem:

1. In terms of physical conditions, water temperature is high for a freshwater river, the water is murky brown to black and emits foul to obnoxious odor indicating a mixture of sewage, decomposing organics and chemicals. Low transparency also prevented the passage of light, although the levels of Total Dissolved Solids (TDS) and Conductivity did not exceed the maximum standards. Eroded soil and organic particles contributed much to the low transparency of water.

2. Dissolved Oxygen (DO) is quite low with majority recording a little above and below the minimum requirements for living aquatic organisms to survive which is 5 mg/L while the best level is between 7 to 12 mg/L. Based only on DO, the water quality is assessed as slightly polluted to gravely polluted.

3. In terms of Phosphate and Nitrate, the levels of the former is very critical and the most likely cause of algal bloom resulting to a condition of eutrophication which is the reason for low DO, bad odor, and few species of aquatic fauna belonging only to two aquatic groups –fishes and mollusks, and 1 semi-aquatic species of crabs.

4. The level of toxic phytoplankton reached the highest in all 5 sampling stations especially at the point-source sampling station.

From among the above problematic conditions, eutrophication and the level of toxicity based on toxic phytoplankton count are alarming because they indicate a dying river where aquatic organisms such as submerged plants and fishes including mollusks die. There is also the possibility that groundwater pumped out from near the river may be contaminated and causing ailments that could not be explained.


1. There is a need to educate people about the current conditions of the Naga River.
2. Cleaning up of the river at this state and maintaining an improved condition require some ordinances from the local government in order to control the causes of the problems
3. Beautify both banks of the Naga River with a design that will make people reluctant to indiscriminately throw waste on the riverbanks and the river water, hence prevent further degradation of the River
4. Conduct regular quarterly monitoring of the river water and biota with the purpose of providing inputs to LGU of the state of the water quality of Naga River, especially in terms of further worsening of the water quality.
5. Create “Bantay Salog”groups comprising of the youth and other volunteers along the riverbanks of Naga River to ensure that ordinances are followed.