Fish are good indicators of water quality since they are very sensitive to contamination that chemical tests may miss, according to a study made by the US Environmental Protection Agency (EPA). The EPA study indicates that using fishponds complement chemical testing done by government regulatory agencies to assess the degree of contamination and toxicity of water bodies, including rivers, streams, and lakes. The Pandacan oil depot - operated by Pilipinas Shell, Petron Corp., and Chevron along the Pasig River - has been using this same process to ensure the quality of every drop of water it releases into the river.

Fish thrive in Pandacan depot's wastewater pond. (2009, September 6). Manila Bulletin, p. 1.