Objectives: Industrial development in Korea results in a rapid increase in the number of chemicals, some of which may be responsible for toxicity to aquatic ecosystems. In addition, the types of hazardous chemicals included in industrial effluents have gradually increased. Therefore, chemical analysis alone is not enough to assess ecological effects of toxic chemicals in wastewater. Methods: In response to new regulations as whole effluent toxicity (WET) tests for effluent discharge of 15 publicly owned treatment works (POTWs) and 25 industrial effluent treatment plants in Gyeonggi-do, which will be effective from 2011, a necessity of studies emerges that investigates toxicity levels. Results: In case of the public treatment plants, none of them had exceeded the criteria for ecotoxicity. As for individual wastewater discharge facilities, on the other hand, two types were found to exceed the criteria: pulp and paper manufacturing facilities and pharmaceutical manufacturing facilities. For the pulp and paper manufacturing facilities, monitoring results could not help determine the exact toxicant identification. However, Daphnia magna inhibition effect or death was found to leave white plums, suggesting that suspended solids treated and the polymer used in coagulant dose. In case of pharmaceutical manufacturing facilities, the general water quality parameters cannot affect Daphia magna. However, conductivity and salinity can have an effect to be 14,000 ${mu}s/cm$, 8.1‰ by salts, respectively. Toxicity Identification Evaluation (TIE) and Toxicity Reduction Evaluation (TRE) procedures results appeared to be effective for identifying toxic compounds in $Cl^{-}$ and $SO_4^{2-}$. Conclusions: It is necessary to develop control measures for water treatment chemicals and salts used for processes such as coagulation in individual wastewater discharge facilities in order to achieve the goal to protect aquatic ecosystems in public waters.